Army of Ruin

Took awhile to get the right character that worked for me but in the end i used Ariana because of her long reach and Shell ability,and then i just focused on getting Wolf's Fang,Toxic Stench,Necromancer Guantlets & Magic Staff,that is all the weapons i focused on,so they cant get to met and i got the staff just for abit of long range for the eels

This should be attempted toward the end of the game when you are strong enough I was 50 hours in and had only 5 achievements left before attempting the no-damage achievement. so what worked for me was I didn't move from the starting page and just focused on not letting enemies get close. No issue the first time doing it with this setup and as mentioned above if you want to check to see if you have been hit press start and under challenges it should say in Challenges Complete the stage without taking damage for that level if it's gone you have been hit. it might be hard to get the same setup but just use what you no works and for me, it was this.

character Ariana
damage lvl 20
fire rate lvl 10
size lvl 10
projectiles speed lvl 10
duration lvl 10
skill max
pickup range max
luck 8/10
health lvl 10
regeneration lvl 12
weapon capacity max
trinket capacity max
projectiles lvl 1
re rolls lvl 8
banishment lvl 4
favorites lvl 4

Favorites were
Weapons: Rotting Coil/Thunderstorm Javelin
Trinkets: Frozen Cross/Magnifier

items I used mainly for damage and size
Trinkets: Forbidden sword/Magic needle/Silver bullets/Spyglass
Weapons: Battle Cog/Bronze Star Fish/Mighty Punch/ Quicksilver Spears from the character Ariana