Curse of Chaos
Once per battle as a free action when a nearby enemy rolls a natural 1–5 on an attack or a save, turn their roll into a natural 1 and improvise a further curse that shows how their attempt backfires horribly.
A curse should have about the same impact as a typical once-per-battle ability. For example, a typical curse might lead to the cursed attacker dealing half damage to themself with their fumbled attack and being dazed until the end of their next turn. The GM may reward storytelling flair and/or limit the suggested effects of the curse.
Whenever a nearby enemy rolls a natural 1 on an attack against you, you can use curse of chaos against them without expending it.