Pandemonium Colossus

Whenever a creature enters the battlefield under
your control, select either creature or player.
Choose an opponent, flip a coin and call it. The
winner of the flip selects a target of the chosen
type, deal X damage to that target, where X is the
power of the creature that entered the battlefield.
{2}: You may sacrifice a creature to ignore the
result of a coin flip, and flip again.