One of my creatures is a Dawn Crusader with a Dryad Naturalist fused into it. During a boss fight, I afflicted Stone to the boss, preventing all damage done to it because it is resistant to it. (I did not know…)
Since Dawn Crusader always Defends after each turn, it will increase the debuff duration by 1 turn every turn thanks to Dryad Naturalist’s trait, basically meaning that, as long as it is alive, enemies will have their debuff forever, unless they can remove it via a Spell. This means that the boss cannot act and cannot take damage, which means that the battle will never end. Especially because I used Spell Lock as well to add a permanent Silence debuff to every enemy preventing them from casting a Spell in the first place.
In case it is relevant: the battle is against Kraynaks.
EDIT: It seems they can still use Spells, but if they don’t have a way to remove a debuff, it still remains an endless battle.