Astral Dragon

Flying, protection from colorless
Before shuffling your deck at the start of the
game, reveal this card. Exile 20 different creature
cards not in the game. Reveal all 20 cards to
opponents. Compose a list where each creature
corresponds with a number between 1 & 20.
Reveal this list. An agreement must be made on
the structure of & creatures on the list.
{1},{t}, Roll a d20. Whichever number is rolled,
Astral Dragon becomes a copy of that creature on
your list and gains this ability.