Warning: This guide was prepared for game version number 21142 (it is the last version before introduction of "The Color of Madness" DLC) and now can be outdated. I will try to update it soon.

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This is the best party for Ruins I've played so far - it's based on video I've found. I wasn't so sure about Leper, so I took Hellion instead. My trinkets weren't the best ones and one of my characters was only level 4 but this party finished long expedition in Ruins with full HP, zero stress and got me Ancestor's Pen as reward. :)

rank 1: Hellion, level 6
- Combat Skills: Wicked Hack / Iron Swan / Barbaric YAWP! / If It Bleeds
- Camping Skills: Encourage / Battle Trance / Revel / Sharpen Spear
- Trinkets: Berserk Charm / Sun Ring

rank 2: Crusader, level 6
- Combat Skills: Smite / Stunning Blow / Holy Lance / Inspiring Cry
- Camping Skills: Encourage / Stand Tall / Zealous Speech / Zealous Vigil
- Trinkets: Berserk Charm / Sun Ring

rank 3: Vestal, level 5
- Combat Skills: Judgement / Dazzling Light / Divine Grace / Divine Comfort
- Camping Skills: Encourage / Bless / Chant / Pray
- Trinkets: Ancestor's Scroll / Feather Crystal

rank 4: Grave Robber, level 4
- Combat Skills: Pick to the Face / Lunge / Shadow Fade / Thrown Dagger
- Camping Skills: Encourage / Snuff Box / Gallows Humor / Night Moves
- Trinkets: Raider's Talisman / Solar Bracer

Nice!

I have made it as far as week 23 with a roster full of level threes

So have you tried my party setup? :)

I have a couple questions for you -

I usually put Hellion in 2nd position and prefer Break Through over Wicked Hack.
I usually put Grave Robber in 3rd position - but I always want Poison Darts. Why would you not have that?
I find that with Crusader in 2nd place, using a move-resist trinket helps.

How are you able to have zero stress at the end? How do you deal with stress-dealing enemies?

Wicked Hack is pure damage skill. Breakthrough is more finishing skill or for the cases when you expect that party will be shuffled around (for example before some of the bosses). I would not use Breakthrough as regular skill as it debuffs Hellion with -20% dmg after its use (unless you have a lot of spare Medicinal Herbs in your inventory). In the party I presented Grave Robber is "dancing around" as anti-shuffle character and also (which is more important) to let Crusader use his most damaging skill, Holy Lance which has some rank requirements so needs some tactical thinking at the start or during the fight. Please note, that if Crusader ends in rank 3 with no enemy in rank 3 or 4 he is kind of "stuck" and needs to waste his turn to move forward or use Inspiring Cry and wait for Grave Robber's Shadow Fade.

Why not Poison Darts? In this party I prefer more pure damage oriented skills. Poison Darts also should be used as soon as the battle starts (for best effects) as it is a DOT skill and on first turn I use Lunge most of the time to let Crusader use his Holy Lance. Crusader from my party does not need such trinket as he kind of needs to "dance" so if enemy push him to rank 3 he probably will be happy to use Holy Lance. :) I'm stalling the battles with two enemies left by using stuns on them (Hellion's Barbaric YAWP! helps a lot here) and then use Crusader's Inspiring Cry for stress recovery.

Also I'm rather not selecting short missions as they do not offer camping. In medium missions I'm trying to end them with camp and in long ones I'm doing first camp somewhere in the middle of quest and the second camp at the end.

A couple spoiler-free tips for dealing with stress:
_focus stress-inducing enemies first, health is easier to refill than stress
_killing blows and trap disarming heal small amounts of stress, keep it in mind when chosing the hero that will deal the last blow to a dying enemy, as well as when ready to disarm a trap
_critical hits heal stress on the dealer as well as random team members, a critical roll on a healing ability will heal both health and stress on the target
_light is your friend, both by reducing the amount of stress dealt to your heroes and by giving higher scouting chances
_a lot of hero classes have good stress-healing abilities when camping, so you can use camping at the end of a quest to heal everyone’s stress
_trinkets and quirks can have a high effect on stress rate, keep it in mind when building a team for a specific quest

Nice to have such a lively discussion!
There are basically 2 play styles for the Grave Robber. Either you stand still and use your ranged skills or you jump around with Lunge & Shadow Fade. Poison darts are a good addition to the first one but don't synergize well with the second. You could still squeeze them in if you really want to and blight is valuale in ruins, but it's not essential for the party setup discussed here.

As mentioned above: breaktrough is usually not a good skill to use for a hellion as you want to single targets out quickly instead of spreading your damage all over (and debuffing yourself while doing so). This holds true for most multi-target skills.

Can any of you do me a favor and post something in my other topic? I think it got some bug as it has -1 replies and it's not visible on topic list... :/ Thanks in advance!

Here is the link: https://www.gog.com/forum/darkest_dungeon/the_wall_party_setup_champion_darkest

Edit: It seems it repaired itself after I typed this post. Sigh, sorry.

I've found quite interesting discussion about Poison Darts which, I think, you also should read. :)

https://www.reddit.com/r/darkestdungeon/comments/860gdi/weekly_theorycrafting_discussion/dw2bjfs/

In addition I'd like to add that raw damage isn't the only thing to be considered when it comes to damage over time abilities. It's often good to have to option to not kill an enemy outright but instead to make sure he dies, as soon as it is his turn. This for example gives your party time to heal up, before the last enemy dies. Blight&Bleed are also good on tough, high-protection enemies so I found this skill quite useful.

That discussion was very helpful. Thansk!