This is probably the hardest mod ever because it has multiple strong mobs and invisible ones too. You will never see the invisible mobs coming for you so watch out! The Champion (The Final Boss) has over 2M Health and Attack Power! Shaders make the mod look better (Optional)
Requires Attribute Fix: https://www.curseforge.com/minecraft/mc-mods/attributefix/files/3801087
Good Luck