A Door

When A Door enters the battlefield, choose one of the following effects.
• Create a 1/2 Human Token which has the following " {t}: Gain {c}"
• Create a 3/1 Nightmare Token
• Exile a creature and give it the following text, " {c}{c}{c}{c}: Remove this card from exile at the start of your next upkeep phase, and your opponent may create a copy of A Door in their hand."