Mercy's habit of taking bits and pieces off the old car she leaves in her backyard to tick off Adam...then the revelation that he used to run around naked in his backyard at night as a sort of revenge.
Coyote's way of figuring out how big the River Devil is in River Marked. He shoves Mercy into said river and uses the length of the tentacles that try to grab her as an estimation tool. Doubles as a CMoA, seeing as he completely ignores a very ticked off Adam while measuring.
In Frost Burned, the fae apparently responded to the US government trying to bomb them by teleporting the incoming bombers to Australia. The incident was embarrassing enough that the US government had to issue a formal apology to the Australian one.