MTGNexus

Did anyone ever play something like this? Instead of having a Planechase-style chaos effect on the game, the chaos deck would be an automatic opponent, kinda like the Theros "Face the Hydra" idea except the "hydra" is a stack of evil junk rares contributed by one or more of the players? If you remember playing something like this, did your variant have a name? cos this is precisely my kinda jam!

also, does anything blatantly wrong with the rules jump out at you? I'm worried about an opponent who automatically attacks in a world of planeswalkers - that seems to require a choice, how would you avoid that?

edit: reasonable stuff that could be in Chaos's deck:
Fatespinner
Altar of the Brood
Lavinia, Azorius Renegade
Chainer's Torment
Clip Wings
Ankh of Mishra
Mire in Misery
Coursers' Accord

meaner stuff:
God-pharaoh's Statue
Butcher of Malakir - assuming chaos's stuff gets a death trigger before it phases out?
Crackling Doom
Overburden
Hollowborn Barghest