Which bosses and skill are one shotting you? The later game bosses do have very high Attack stats, so make sure you're also gearing with Defense and Resistance in mind.
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But I have late game gear, and some enemy attacks deal 50 dmg and some 26.000.
An example would be the slime Dragon in the depths, even when slime logged one attack dealed 13.000 dmg on resistance. I had to reset the fight for the right RNG about 7 times until i was able to kill it within 2 turns and without being killed. The slime Zealot was similar.
Sorry that the answer took so long, had some issues with itch for some reason. I am not able to reply with a picture. Here are the stats and setup for the oneshotting issue that have:
HP:3794 MP:702 attack:424 def:214 Magic:298 Resistance:262 agility:296 luck:149
Minotaur Axe
Stone Gauntlets
Ocean Guards Helm
Hot Pants
expansive amulet