Thousand-Faced Shadow Bug: Intervening 'If' Not Checked On Resolution?
Playing against an opponent who had two creatures out, and I could block neither of them. Before damage, they Ninjutsu'd in a Thousand-Faced Shadow, targeting their other creature.
I had a burn spell in hand to kill the shadow that wasn't big enough to kill the creature they wanted to copy. With the Shadow's trigger on the stack, I attempted to kill the Shadow. In response to that, they cast March Of Swirling Mist, targeting their Shadow. The Shadow then phased out (so no longer attacking, or 'on the battlefield' at all). Then, my burn spell fizzled, and the Shadow's trigger resolved, creating a copy of the targeted creature.
Afterwards, I asked the Magic judge chat to be sure, where they confirmed that since the Shadow was no longer attacking, the trigger should've failed to resolve.