Before I begin: I've just beaten the first boss, so I might be missing aspects of the game that unlock later along the line.

Suggestions and ideas:
- It would be nice if we were able to select items to not drop. I have unlocked a bunch of items in order to give them a try but now I've not only wasted progress points (dead cells you could say), but they are actively getting in my way to progress. I would much prefer it if the exploration of new weapons would be rewarded rather that penalized.

- In the same vein: More often than not I prefer the rusty blade over whatever starting weapon awaits me. Could it be hidden a little closer to the first door, please? (Maybe under the step right next to it?)

- The following suggestion contains a spoiler for the first 10 or 15 minutes of the game. If you haven't played the game yet, consider skipping this point. Also consider buying Dead Cells. It's already really good!
Something conceptual: It is my understanding that the protagonist gets healed by the nutrient fluid from the alembic/breeding trough between levels because they are a homunculus as well. But even if they are not: It seems needlessly cruel to kill a (fellow) homunculus by draining all of the fluid - especially when one only needs to top off HP. Maybe if the protagonist's healing potion still had all of its charges, they could hold their head under the tap and only drain half of the fluid, causing the homunculus' light to grow dimmer, but not get extinguished.
In my mind this would also add incentive for the player to do well.

Bugs:
- Fast attack animations cause the protagonist to stop briefly in midair. When I wield a very fast weapon and hit attack really fast, it causes the protagonist to hold their position - in midair. That behavior is confusing to me and I find myself having difficulties to adapt my combat style. It causes me to miss a fair bit of my blows whilst jumping, which go right over the enemies' heads. It doesn't affect me all the time, but in panic situations it's easy to forget that the game behaves this way.

- Something very minor: When a dietary path is switched in the middle of a run while standing next to an item, the item's icon is updated. But the item's text box only updates once the protagonist moves away and towards it again. Could it be refreshed when the path is switched?
(I'm aware this affects only a tiny fraction of the players and probably only once or twice, but it might be easy to fix.)

Suggestions and ideas - Hunter's Grenade:

Let me describe the problem I see first.
Having used the Blueprint Extractor successfully multiple times it still fails me more than half of the time. I feel like the main issue here lies within the documentation:
- The unlockable is described only very vaguely, which caused me to check every block of the starting area twice before it dawned on me that the grenade might be within the combat area of the prison.
- Using the skill unsuccessfully made me wonder if the skill was actually implemented, because it threw the skill. Something that, to the best of my knowledge, no other skill does.
- Using the skill successfully for the first time was quite the surprise: I thought the enemies' damage or their speed would increase - not that they would transform into a full fledged elite. I also missed out on the fact that there was something called a Blueprint Extractor on the floor. Thinking back to that moment I would argue that it went unnoticed because a freaking elite spawned about an inch in front of my face. This caused me to waste the grenade the first time, which left a bitter feeling in my mouth.
- Also: Who the eff has time to figure all this out, let alone read anything, in the middle of a combat with an elite?
- And like I said above: Sometimes holding the skill doesn't work.

My suggestions would be to either:
A) Have the skill work similar to a regular grenade if it doesn't work. Remove it from the skill bar when it works, instead of having the skill drop. Simply have the enemy drop the blueprint on defeat and leave out the whole Blueprint Extractor bit.
B) We get an essay about the game being in early access every time we start the game. Maybe a few more lines of documentation for the unlockable and the grenade itself wouldn't be amiss. Walk the player through the entire process.
C) If for some reason you'd want to keep the skill in its current form, the player should at least get a tutorial area after unlocking the grenade. Within that area a group of target dummies would await them in order to figure out how this skill works. (You already have the skins for target dummies so the artists wouldn't have to work on this.)

1) I kinda agree with that. Some weapons are just bad and I do not mean only damage. As far I know option to refresh content of the shops was introduced not so long ago to somehow counter this. This works most of the time, but often I don't get any weapon shop at all (especially on route to the Crypt).

2) I don't see this as a bug. Sometimes it helps, when you use fast, but low damage dealing weapon against flying enemies or even against The Watcher. Even with this feature, hard hitting weapons are preferred in current meta to my understanding.

Oh, I have no doubt that this behavior has its uses, but it still seems pretty counterintuitive.

As for "the current meta": I have tried the hammer, the zweihander, a multitude of bows, whips, ice blasts, force lightning and the lot, but a fast sword/knife with a shield feels the most natural/fun for me. So that's what I can give feedback about with a degree of confidence.

And if anybody is stumbling about my line about the rusty blade as a preferred starting weapon: You can save some running by ground smashing right next to the block with the rusty blade in it.

The Watcher:
- This might be a personal problem, as I don't have the best reaction time, but the 'racing tentacles' are so fast that I find it physically impossible to jump over them or roll through them. Even if I spot them the very instant they enter my screen, there's not enough time for my character to finish a combat animation and get its ass into gear.
- The screen constantly zooms in and out. While this might have been an impressive feat on the technical side of things it makes the whole fight... uncomfortable from a gameplay perspective.

I'm not familiar with the entire development history of Dead Cells but my suspicion is, that this fight was at one point designed to show the entire boss room and that the zooming was added later. This boss fight differs greatly from the rest of the game (at least the bits I've seen so far): It is a slow fight in which the players are rewarded for taking their time, making careful decisions instead of rushing it. It is often better to skip an attack in favor of a better time window. But at some point the player has to attack and that time is not much of a informed decision when they only see half the battlefield. It feels like playing chess with half of the board obfuscated.
In short: I think the Watcher is an interesting boss, but the encounter would work much better if the camera stayed zoomed out during the entire fight. The difficulties I described above seem less by design and more the unforeseen side effects of some updates.

This kinda of spoiler, but Bear Trap is kinda OP against tentacles - I killed The Watcher few times using low level gear thanks to Bear Trap that makes whole fight a lot easier.

Don't look for when they enter, look for when a cloud of dust on the ground leaves the screen at high speed. There'll be a racing tentacle comming from that direction quickly afterwards.

Thanks to both of you for your advice! :) I agree: The Bear Trap is OP against almost anything - mainly because enemies in a Bear Trap can't turn anymore. It took me forever to notice that. Unfortunately I've unlocked a lot of traps, so I can consider myself lucky if I get some rotating sawblades, an ice grenade or something similar topical. I hadn't noticed that they start speeding up whilst still underground.

While I don't want to burn myself out while a game is still in development I still do a run/attempt or two on days I find some time. I'll make sure to apply what you've told me and then get back to you. Again: Thank you very much for giving advice.

Hello you beautiful people!
Since that last time, I've had some opportunities to test looking out for fast moving dust clouds whilst also having bear traps at my disposal. I've also had at least one reliable source of freeze available during those runs and was able to reach the third wave of unwanted tentacle violation during the Watcher fight. Those are a lot of very fast tentacles, but I feel I might get there. Thank you very much for your advice.
(And for Motion Twin: Still not a fan of the whole zooming business during the main fight, to be honest, but it's much less of an issue for me, after having spoken to more advanced players.)

There is also two other things I was meaning to bring up the last time:
Suggestions and ideas - UI:
In the main menu, pressing up whilst on the first menu point does not bring the cursor down to the last point (Quit). Every other menu I have encountered in the game loops around. While this really is a minor nitpick it gets me almost every time I quit the game. So the very last thing I do when ending every single session is getting mildly irritated at that menu. I feel it would be easily fixable but would affect a whole bunch of players, so I brought it up.

Balancing - Potion Level 4:
I currently got as far as the Watcher, where I hit kind of a a brick wall. I know there is at least one more boss, but if the Watcher was designed for players with a level 4 health potion it took me pretty much exactly 200 cells longer to unlock than I would have been comfortable with. And I started investing the cells as soon as the upgrade became available.
Please note that I don't necessarily thing the upgrade is overpriced. But the time of my progress stopping noticeably and there being 200 cells missing on the upgrade coincided so noticeably that I can still remember it vividly 2 weeks later. Making the 4th potion upgrade available earlier would also have made a difference.

---

Balancing - It would be nice if we were able to select items to not drop. (Supplement):
At the end of last year, I've spend a few hours on a new account. I have unlocked all the random starting gear upgrades, the bleeding sword, health potion level 3, the level 3 purse, both recycling upgrades, one random shield (to be able to reach the level 3 health potion) and no Hunter's Grenade. If given the option I would have opted for the oiled sword rather than the shield, but I didn't get the blueprint.
Upgrading in this minimalist fashion has brought me to the depressing realization how useless all those fancy blueprints are to me. I went for a build with a quick sword/knife/dagger in main and the freezing spell in the offhand. Bear Trap and freezing grenade as active skills - or two Bear Traps, if I feel like it. It's a bit slower as a build, but it's pretty save and methodical most of the time.
The only things I really miss are the 4th potion upgrade and the rainbow of unlocked items I see in the Prisoner's Cell at the start of every run.
I know it's impossible to balance skills and weapons whilst giving them a great mechanical variety. But I would prefer to be full of joy after receiving a new toy/blueprint, rather than feeling indifferent about it. I am a player that loves shiny stuff! Honest! But I would love it much more if it wouldn't remind me of how useless it was to me...

Suggestions and ideas - Cosmetics:
In the vein of having no feasible options to dump cells into (I also ran out of spending options on my main savegame), have you ever considered adding cosmetic options as an endgame cell sink? Like dying the homunculus' slime pink for 1,000 cells? Or gold? Or dying the prisoner's attire green for 400? Or a color that isn't red/green, for players with that particular color vision deficiency. Like black. Or pink... :)
I mention this because I drop like 50 cells every time my homunculus' body gets desecrated which makes me feel bad and probably looks bad in the statistics for players who care about those.


[Edit:]
Formatting issues.

The 0.5.11.1 update just rolled out.

Changelog:
GOG's current changelog doesn't reflect the cornucopia of recent updates to the game.

Special Note - The Collector: Either I unwittingly ingested a substance outside of the game or the speed at which the upgrade bar charges was altered. It didn't become a mayor issue, but those are the kind of things I'd like to know about in advance. (It could have become an issue because of the way that unlocking blueprints can be a downgrade.)

Bugs(?):
Frantic Sword: The Frantic Sword is by far the loudest Dead Cells weapon that I ever yielded. I hadn't unlocked it before the update, so I thought I should let you know in case this is a new issue.
Prisoners' Cell - Map Generation: In one of my runs I combed the cells twice but couldn't find the second scroll. All monsters were dead and no door stayed unlocked... Unfortunately I forgot to write down the level seed, which I only remember now is a thing.
The Promenade of the Condemned - Map Generation: In the map "4a8c1404c #65800 C3" shortly before the middle of the map there's a house generated where the player has to awkwardly open the door before they can climb inside (from the west). Having a 1 block wide platform or a narrow ledge generate on the west side would smoothen out that building block.
The Promenade of the Condemned - Map Generation: In the map "4a8c1404c #868222 S4" near the end of the map there's a carrot in the wall of a... "square shaped hole inside of a house" that I could not pick up.

UI:
The Collector #1: The borders of the selector don't match up with the borders of the selected fields.
The Collector #2: The interface doesn't loop around anymore.
The Collector #3: Upon handing in new blueprints, said blueprints get focused only for less than a second before the focus goes back to the first item in the list. Either let the focus stay where it is or don't move it at all. The current situation is the worst of both worlds.
Dropped Items: The "Hey! Look! Look! Look! An item dropped! Right here! Right here! Right here!" effect is maybe a tad bit too flashy. On some occasions it also lands in a different spot than the item itself, which looks a bit... curious.

Personal Comments:
Potion Refilling: I instantly noticed that you sped up the potion refill animation. While I had no issues with the speed for that animation I can imagine more invested players will greatly appreciate this.
Balance: The early game got harder for me as a direct result of the latest update. Even if I spread some points into survival and tactics, I feel much more squishy than I felt playing before this update. As always it might be because I suck at the game, but I thought I'd let you know. I'm assuming that feeling will be less present after handing over about 500 cells to the forge person. On the flip side the Clock Tower got noticeably more manageable for me and I cleared that level for the first time.
Balance - Ygdar Orus Li Ox: I think making the Ygdar Orus Li Ox available on every run helps balancing the game. However it would be nice if the Mutation Trader interface had a note that this mutation will only be available between certain levels. This would especially help new players who aren't familiar with the historic context and would wonder what the hell...
Mutation Trader Animation: I think it's cute that the Mutation Trader hops into their own rucksack. But why does the trader do it? Don't get me wrong: I want to keep the animation, but I feel like I'm missing some narrative here? Is it kind of an inside joke?
The Promenade of the Condemned - Tower: There's a new tower near the middle of the map containing a rose shaped key. As far as I can see it's connected to a shiny new bow blueprint. However I don't have the... rune that lets me traverse vertical shafts (I avoided spoilers so far, so I don't know its proper name) and that probably won't change until I've beaten the Watcher. I appreciate the hint, but could those elements maybe not appear in every single Promenade of the Condemned map while the player doesn't have that rune? I find it a little demotivating.
Gem (starting area): Thank you for removing the gem in the starting area. It added tedium to each run but I had felt bad before when I didn't pick it up.
Gold: Gold (and by extension the various purse upgrades) now feels more useful/"valuable" to me than before the update, simply because of the reset option at the Mutation Trader. Sometimes it's the little things. :)
Clock Tower: Spoilers ahead! I'll try not to spoil too much for readers who can't help themselves, but still: Spoilers! There is something within the Clock Tower that I would consider "a puzzle kinda". I disliked it strongly. The main reason for this was that I had to interact with something I had considered interactable solely for cosmetic reasons. If that type of object had a more prominent coloring on the interactable part, I would have thought about it more. I've spent "well over 30 minutes" (I wouldn't admit how long this actually took me) running in circles and checking every wall until I figured that one out. I would have enjoyed that time far more had there been a puzzle that made me use my brain instead of a puzzle that consisted of "spot the things hidden in plain sight".
Fog Fjord - Door Signs: Not having to look at the map anymore to see those is greatly appreciated!
Enemies that drop scrolls: I feel like enemies that drop scrolls slow the flow of the game down because the players has to look out for them - which seems to be a very different direction from previous versions of Dead Cells. (Each session being so [relatively] short was a selling point to me, which I also brought up when telling my friends about the game.)

Suggestions:
Mutation Trader - Ygdar Orus Li Ox: If a player resets their Mutations whilst having a Ygdar Orus Li Ox still available, the Ygdar Orus Li Ox stays locked in the selection screen. This made me sad. Could you maybe enable it again in those special instances?
Gender: There's not enough gender variety in the game. Can the player character please randomly take over a female/more feminine body? I can't imagine only males would get executed in the world of Dead Cells...
Map Seeds: A button on the map screen that copies the current seed for easy pasting into forums would be a nice gesture towards testers.
Forge: Could you add the Rusty Sword to the Forge's list of upgradeable items? It would have been al least my first upgrade target because I often prefer the Rusty Sword over the random starting weapon. I would ask for the same treatment for the wooden shield, but personally I prefer any shield to the wooden shield and I'm not big on bows. It's hard to justify a request for the shield and bow when I wouldn't even use the option myself. (I don't want to deny others the right to make such a request, here or elsewhere - I just wouldn't make it myself.)

UI:
Bosses - Health Bars: Something I wanted to bring up several times and always forgot: Could we get the option to display the bosses' regular health bar as well? The big health bar on top of the screen might be more precise, but it's also way out of the way from everything else that's happening on the screen.

Balancing:
General Thoughts: I have spend a great deal of time exploring the latest update over the weekend. Although I mostly adapted my initial impression holds true: Even after a bunch of forge upgrades, the homunculus has become rather squishy during the early levels (Including the Black Bridge) but noticeably sturdier in the Fog Fjord and the Clock Tower. Weirdly enough I also feel even squishier than before in the Old Sewers which have a tendency of chewing me up quite a bit. (I'm unsure about the name: The brown ones.) It feels as if monsters in these zones had their damage buffed considerably. I'm concerned that this might have raised the required learning curve for new players a bit too steep.
Assassin Vs. Watcher: After the update I had my first 3 encounters with the Assassin and 2 encounters with the Watcher, which I have grown quite familiar with over the past few weeks. So far I haven't beaten either of those bosses, but I'm making great progress on the Assassin, bringing her down to about 40%, 30% and <10% respectively. At the same time my progress on the Watcher stays about the same. This seems odd to me, because I would have expected the Assassin to be the final boss of the game. Maybe I'm wrong about the order or maybe it's something that only happened to me, but I thought I'd let you know.
Trap Cooldowns: The reduced skill cooldown mutation makes using active skills much more... usable, during regular levels. Before the Forge Upgrade I mostly carried traps around as good luck charms, rather than usable items - outside of boss encounters. The cooldown used to take so long that I never utilized them in order to have them ready "in case of an emergency". Would you consider lowering at least the trap cooldowns specifically permanently?

Bugs:
Fleeing Camera: There were several instances for me when the camera went way past the action. It mostly happens when there where multiple things happening at once. (Like being shoved whilst trying to move - and other things that tend to happen whilst being surrounded by 4 or more different enemies.) Before the forge upgrade having the camera running away from me was something that very rarely happened and mostly whilst jumping. I say "mostly" but it was less than 5 times ever since the GOG release. Not really worth mentioning... The new fleeing camera did so more than 5 times over the course of 2 very active days.

Suggestions and ideas:
Cosmetics (Important Addendum): In a post above I suggested dying the homunculus' slime pink or gold. I'd like to add a specific suggestion to that list and I don't know why I didn't think of that one before: Cornflake Homunculus! (With kind regards to Jim Sterling.)
GOG Goodies - Wallpapers: The cover/banner for Dead Cells looks very nice. Alas the biggest GOG banner we can download comes in just one resolution and the title on it is a little too big to look good on a wallpaper. Being limited to the experience of someone who only uses MS Paint for such things, I was wondering if it would be feasible to invest some time into making a wallpaper (with a few different resolutions).


[Edit:]
The usual struggle with GOG's premium forum technology...

(Still concerning the 0.5.11.1 update.)


Bugs:
Screenshots: If the game saves screenshots on its own, I'm unable to find the folder, so right now I press Print on my keyboard, open a bitmap, paste my screenshot there (and convert it later). However, taking screenshots this way only works in windowed fullscreen and only once. What I mean by that is that every screenshot I take after the first one comes out black - unless I change to fullscreen and back to windowed fullscreen as a workaround. Could we please get a regular screenshot function?
The Assassin: When the Assassin tosses the Homunculus around, the camera lingers on the Assassin for too long (little more than a second) before it suddenly seems to remember that there are two participants in this fight. Like with the Watcher it seems that this encounter was designed for players who can see the entire room. (This became a crucial issue when I couldn't see my character and accidentally chugged two health potions instead of one.)


UI:
Boss Source Cells: Could you please add the word "PERMANENTLY"™ somewhere to the texts when the Homunculus absorbs(?) a Boss Source Cell? I was so afraid I had to do all of this again when I inoculated my first cell. Also please consider adding a note to the... inoculation station(?) stating that the cells will not be consumed/used up in the process. Notes like that would have saved me a lot of negative stress and would help other players avoid negative stress. Thank you.
Forge - Filter: An option to "Hide Unavailable" would be a useful addition to this window.
Forge - Item Information: The Forge offers remarkably little information on the upgradeable items themselves and there is a large empty spot on the right-hand side of the interface. That spot would be ideal for showing the basic item descriptions. This would be handy in cases the player can't quite remember what does and does not apply bleed - for example.
Forge - Upgrade Information: And while you're at it, "Bonus to quality level 2" is not much help. In fact, even removing that text und just leaving the upgrade buttons would be an upgrade. Remember that items are also labeled "Bear Trap II", "Bear Trap III", etc. - suggesting a downgrade, if a player currently holds a "Bear Trap III". I would suggest adding boxes for two items instead: A comparison of the current item quality and an example of what the upgraded version would be like. And an arrow in the middle. That should work as easy to understand instructions for all ages.


Suggestions:
Autopause: It would be nice if the game would automatically go into pause mode when the player tabs out.
Monster - Gargoyle: If you are ever in need for new monsters, gargoyles would be a nice fit for the game. I might be biased, though, because I quite liked the Gargoyles TV show...
Assassin - Teleporter: The Assassin has teleporter before her room that doesn't connect to anything. Might be canon, though. Who am I to judge. Maybe it was installed by the same company that installed the defective teleporter platform in the Mars Pyramid in Zak McKracken and the Alien Mindbenders...


A small comment for other readers:
Just for the off chance someone other than the devs actually reads this far while trying to make up their mind if this game is worth buying. To me, it absolutely is. There are several aspects of the game that would still require work. Since the game is still in development, those improvements might still see the light of day. But even if they don't: Buying it at 25%(?) launch discount, I would still say the game has been good value for me.

(Still concerning the 0.5.11.1 update.)

Bugs:
GOG: The latest update (0.5.12) did not get highlighted by GOG - at least for me. I only became aware of the latest patch when I saw the update to the Changelog thread here in the forums.
Stats Screen - Monsters: The picture for the "Sick Worm", "The Watcher", "The Watcher's tentacule" and "Lure" are missing. "The Watcher's tentacule" should probably read "The Watcher's tentacle". The "Host zombie" has the wrong picture. "Lure" should probably not be here.
Blueprint Extractor/Hunter's Grenade: I used the Blueprint Extractor at the moment I was supposed to in the Graveyard on a... Zombie that explodes into... flying heads. The zombie exploded, but I got no blueprint. Reaching the Graveyard specifically just to throw a Grenade, beating the monster carefully down to 40%, succeeding with the extraction and then having to leave empty handed is not a good feeling. I hope you can figure out what did this before the full release.
Bug(?) - Graveyard: On the map "4a8c1404c #576505 V21" there is a door generated that has a rewardless room in it. (If there was an Architect's key in that room in this particular instance of the may, I did not find it that time.)
Connection to server failed: By the time I write this, there are three things in the game I have yet to see: The exit door of the Forgotten Sepulchre (I get just behind door 2 by now), The bit behind the Architect's door in the Graveyard and the Daily Run. One of these should be way more accessible.


Balancing:
Map design - Watcher shortcut: I was a big fan of the door to the Watcher (removed in 0.5.12) requiring only one active boss cell instead of 3. One of the mayor drawbacks of tackling both that boss and the Graveyard zone is that it takes so long to get there. The Graveyard is a big labyrinth and by the time I reach it, via the regular route I'd be almost in the Assassin's chamber.
Heavy Turret: This is not only the turret to end all turrets. This turret and the Bear Trap are actually the active skills to end all active skills. I have used the Bear Trap with lots of other skills before, but the Heavy Turret is just too useful. It tanks, has about three times as much HP than the Homunculus would have at the end of the game, blocks the Assassin's projectiles, is too small for many regular monster's projectiles to hit it and it works even at a distance that is surprisingly close to the edge of the screen. Oh yes, I almost forgot: It deals more or equal damage to any bow and grants a +15% damage boost. I'm sorry to say this, but in its current form, it's just too strong. All the time you spend designing and implementing other unlockable skills just seems wasted at this point. There are several things I would suggest to nerf the Heavy Turret:
1) Increase the height and hitbox of the turret to 1.5 or 2 blocks. All ranged monsters should be able to shoot back at it.
2) Let the Assassin's ninja star projectiles pierce through at least one target.
3) Currently, regular monsters seem to aim for the nearest target. If the player changes platforms, not many monsters can do anything about it, but I've seen turrets swarmed by 8 or more flying enemies. Maybe flying enemies should either ignore turrets unless the turrets attack the monsters directly - or split their attention 50/50 between all available turrets and the Homunculus.
4) Reduce the turret's HP. Even if the Heavy Turret gets attacked by 3 monsters dealing heavy damage, it outlast all of them without even losing 1/3rd of its health bar. And it certainly outlasts even its regular cooldown. It doesn't need to become fragile, but seeing it break every now and then wouldn't be so bad. So I'd suggest a reduction to 1/4th of the current HP.
5) Reduce the turret's knockback. You know those little ninjas that do a charged backstab? Set a heavy turret up and watch them getting shot into pieces before they can even reach the turret.
6) Reduce the turret's bonus to dps. The turret would be awesome, even if it didn't grant that bonus at all. At least it shouldn't be that big.
7) Remove the possibility of this turret receiving the "Pierces all enemies" trait. This wouldn't change much against the regular monsters and piercing one target is already plenty of speed up.


Suggestions and ideas:
Version Number: Display the current version number in the main menu. Currently, only the version's date is displayed.
Suicide? But how?: The stats screen suggests that there is a way to commit suicide. If this is not a joke or a very well hidden easter egg, I would like to know how this is done. The keyboard setting offer no such option.
Inoculation Station: All levels of increased difficulty read "Increases the level of the Foundry". While this is technically true, it could be worded in a more transparent way. I'd suggest "Increases the Foundry to level 2" (for difficulty +1 & +2) and "Increases the Foundry to level 3" (for difficulty +3). This would get rid of the double "the" as well.
Scrolls: I'm trying to phrase this carefully, but the language barrier might make this sound wierd: If it doesn't break the game in the form you want to make it, having a little message pop up when the player found the last scroll in a level would be a neat feature.
Main Menu - Warning: I get that "Playing Dead Cells with a controller is strongly advised!" Thank you. I've read that often enough and I'll definitely not buy a controller for my PC. Can I please get a checkbox or something to hide that warning? It makes the main menu appear rather aggressive, if not outright hostile...
Ingame Achievements: You could enable independent tracking of achievements for the only person that cares about them anyway: The player itself. Terraria has that system as well: Achievements can be earned and displayed independently of platform or internet connection. You could also use such a system to synchronize achievements after the connection to the servers got interrupted. Or for porting achievements to and from Steam, for players who bought your game twice.

The key is hidden elsewhere in the level. Those "empty" rooms are seemingly just random chance spawns.

Thank you, WingedKagouti. :) I already found the key earlier today and came here to update the post.