Merfolk Trickster and Ghitu Lavarunner
After being targeted by Merfolk Trickster's ETB effect, Ghitu Lavarunner's power does not shrink to 1. This happened to me twice in this game and resulted in two very bad blocks I was forced to make.
I've made this particular play many times, especially on Arena, and unless I am misremembering terribly, it resulted in the Trickster being able to profitably block and kill the Lavarunner.
I am open to being wrong because layers are complex, but I was 99.9% sure the Lavarunner should've shrunk.