Lake god: get 100% physical evasion, this lets you avoid the rampage spam
Thorn princess: just do more damage, are you stacking buffs and debuffs? On buffs you can stack attack++, phalanx, madness, and resins. Mutilation too, just be careful you don't kill yourself. For debuffs, oil (avoids waking her up) or freezing magic bullet and sin burst. If you really can't outdamage her healing, hit her with feeble (undead killer shroom or treponema). Unless you are in the boss rush, you can also charge up frumious wrath from bandersnatch sword. Some other attacks that are strong are han's normal attack, blood edge, zex sturm, deadman's blow, helbreath sword.