The Hippodrome

You may target any creature with The Hippodrome's chaos ability. Whether its power is 0 or less isn't checked until the ability resolves.

If an ability of a plane refers to "you," it's referring to whoever the plane's controller is at the time, not to the player that started the game with that plane card in their deck. Many abilities of plane cards affect all players, while many others affect only the planar controller, so read each ability carefully.

Creatures may have negative power. For example, a 3/4 creature that gets -5/-0 becomes -2/4. The total of its power and toughness is 2. It would need +3/+0 to raise its power to 1.

A face-up plane card that's turned face down becomes a new object with no relation to its previous existence. In particular, it loses all counters it may have had.

A creature that would assign 0 or less combat damage (due to having power 0 or less) doesn't assign combat damage at all.

A plane card is treated as if its text box included "When you roll {PW}, put this card on the bottom of its owner's planar deck face down, then move the top card of your planar deck off that planar deck and turn it face up." This is called the "planeswalking ability."