This thread is to discuss those special moments or enemies in games that you rather want to punch yourself
in the face than facing them.

To start off, mine would be in Xcom: UFO defense.

Picture this : you have completed a good number of missions and you have made good advancements in Tech and weaponry. Sure, a couple of soldiers have died, but you are doing great and the world is happy with your progress.

Then, you get a signal, aliens are attacking a city. "Business as usual" you think to yourself. You get there and you
see This there greeting you. Then this thing, in turn 1 no less; gets a soldier and zombifies him. Then you see to your horror, more of these things. A few minutes later, most of
your team is either dead or a zombie. So you have no choice but to abandon Florida.

So in conclusion, Screw Chryssalids.
Same thing goes for the Lobstermen in Terror From the Deep

First time I encountered a Forgotten Beast in Dwarf Fortress. There I was mining for iron and engraving my hall when all of a sudden, bam! Some terrifying multi-legged, horned monstrosity that squirms and fidgets and has poisonous blood shows up. I freeze in terror as my entire military dies fighting it. I cackle gleefully when I manage to crush it in a quickly thrown together death trap. I realize that the blood seeped unnoticed into the water system. I watch in despair as my entire fortress turns into a rampaging orgy of death as everyone goes insane, strips off their clothes and runs around killing each other.

At the time it was combination of horrifying, NOPE, and whyyyy?!
In hindsight it was hilarious.

Trying to click a player in BloodBowl but clicking "end turn" instead. Well, third times the charm and ive got the community pack installed now to move the button elsewhere.

Yeah, early middle part is the most difficult in both X-COM games you've mentioned. "You got to know when to hold 'em, know when to fold 'em. Know when to walk away, know when to run." But then you will get a better hand (flying suits in this case) and you're back in the game ;)

I don't think you can beat the game without losing any battle. That's the beauty of non mission-based strategy games - losing a few battles doesn't mean you can't win the game. On the other hand those games tend to be more difficult because at one point you may realize that, despite your initial feeling, your performance was not good enough and your only option is to restart the game. I know what I'm saying because quite recently I've decided to replay this game and even though I knew it quite well (from the past playthroughs) the first two attempts were futile. Right now I'm making final preparations to assault Cydonia so the game is beatable...

The worst case (and my least favorite) is Apocalypse because they decided to implement dynamic difficulty there which is absolutely horrendous: the better you perform the more difficult enemies you'll encounter. If you win two first missions flawlessly in third one you may encounter species that were supposed to appear much later in the game (it would be like meeting Ethereal or Muton in the third mission!). This was a terrible idea, because the best winning strategy is to perform below-average all the time - you will be able to expand without losing too much funds while your enemies will remain rather weak. I can't imagine why somebody thought it would be a good idea to implement such a difficulty mechanism that severely punishes you for being good and efficient.

Yeah, thats why the original Xcom is great. I did not know about that Apocalypse difficulty thing, that's just wrong.

But hey, at least it's not TFTD.

Cliffracers!

Heh, you know there is a funny thing there but... Terror from the Deep is actually my favorite X-COM game ;P I know it's kinda masochistic with its huge maps and explosions everywhere (nice picture!) but so it is. I think the main reason is that it was the first X-COM game I've ever played and nostalgia is a cruel mistress ;) Although when I try hard to put my feelings aside and be more objective I'm willing to admit that they overdid TFTD and its difficulty and therefore UFO defense is a better game

I actually like TFTD. The game grows on you, difficulty and all. Cruise ships are still my bane though.

Biggest nope : Terror missions during the night.

My bane wasn't so much Chryssalids. In the early game my bane was cyberdiscs during terror missions. Sometimes I'd encounter like 7 of them on one map, and due to their flying ability they could hide in weird places where I didn't expect them. They are the reason I started to equip at least one soldier with a Rocket Launcher with multiple heavy rockets. It got better though once I figured out how to always play a terror mission during daylight.

Later in the game, aliens with blaster launcher became my bane. Ugh, I haaaattted those things - rather the game didn't have them at all.

Also, soldiers constantly getting mind controlled...

EDIT : another two big gaming 'nope's : Those screaming spiders in Ravenholm, and, 'The Cradle' from Thief 3

Ogrim under the bridge east from Balmora and Ft. Moonmoth.

I encountered Ethereal much later and I didn't offer my soldiers for snack. Maybe a luck however I like Apocalypse the most because it gives you more options and it was more organic to take care of city instead of world.

Plus, religious fanatics. The first time I faced them was big NO and then some more :D. Their strategy was suicidal, so every time when they got closer to your soldiers, they throw a devastating grenade. Instant death was garanted.

Praetorians in Mass Effect 2 got me sweating and swearing. Make a contact and you are dead. It was also moving quite fast and smaller units that were flanking you were coming on the field. And your first encounter was quite early in the game.

There is definitely more but I can't remember right now.

PS. Oh, Chryssalid. My first mission in the reboot was a massacre. I reload it so many times I don't want to even try to count. In the end almost everyone was badly injured but I made it without a corpse in my team.

Anything that feeds into the perfectionist mindset where you can easily permanently miss / fall behind on something with no recourse. Current offender: HoMM3's permanent stat bonuses. Suppose you have only that one last castle to take and it has a bonus-granting structure. I have to get all my campaign heroes to haul their asses there (but not too close), lure the enemy hero out of the castle, storm the castle and hope the enemy doesn't do a suicide-rush.
(Which is only half as annoying as accidentally winning the mission.)

Silent Bomber, PsOne, by the end.. A chess map for the last boss, never got to win this "battle".. Any insane difficulty like that, and big games without a map. First Overlord was bordering to frustrate me for that, good it was rather small and simple areas.

FTL Advanced Edition, round one week ago:
Somehow perfect run with the Stealth Cruiser, but never found any advanced weapons at any store. I knew, this would make it impossible to win the final fight just with weapon power (wouldn´t been able to get through more than three shields); but gladly I´ve managed to get a HackingSystem.
So first stage wasn´t any problem at all, just hacking Shields and then using beam-weapons to quickly destroy them.
But then, the second stage. And I´ve totally forgotten that Defense Drones are also able to shoot down hacking drones...
I´ve just been thinking "Ahhhhhhrg", as I realized every chance of winning was actually gone...

Lobstermen weren't that bad. Tentaculats and Hallucinouds, on the other hand, freaked me out. Also, the Xarquid unexpectedly waiting for me behind a door terrified the shit out of me ;__;