I was playing Plat league, against sir floyd's mono-death deck. He played an Arsenic, and an animate weapon, when the arsenic proceeded to... disappear. It did not appear on the board, and had no effect (see 2nd SS) on the game. Unfortunately this happened too fast for me to get a SS of him actually playing Arsenic+AW.
No instakill effects could have occured in a mono-death (and AI wouldn't do that anyway). Immo, catapult are ruled out, and I certainly didn't kill it. He cannot have RTed it, nor could I.
So:
Game proceeding normally
Opp plays Arsenic
Opp plays Animate Weapon
Arsenic disappears
Game continues as if arsenic was never there.
Never seen anything like this happen before. Confused.