I had a 2/1 Tidus, Blitzball Star on my battlefield. My opponent resolved Poison the Waters choosing to give all creatures -1/-1. My Tidus died and went to the graveyard as expected, but a copy of Tidus was left on the battlefield displaying as a 1/0. The Tidus still on the field was not clickable, and the game treated it like it didn't exist, appeared to be just a strange visual bug.