Celestial Gatekeeper

Whenever a Sliver deals combat damage to a creature, destroy that creature. It can't be regenerated.

Flying 1: This creature loses flying until end of turn. Provoke (Whenever this creature attacks, you may have target creature defending player controls untap and block it if able.)

Flying 1: This creature becomes the creature type of your choice until end of turn. 2UU, T: Choose a creature type. Each creature you control becomes that type until end of turn.

At the beginning of your upkeep, sacrifice this creature unless you pay GG. Morph 7GG (You may cast this card face down as a 2/2 creature for 3. Turn it face up any time for its morph cost.)

Morph 2U (You may cast this card face down as a 2/2 creature for 3. Turn it face up any time for its morph cost.) When this creature is turned face up, you may turn target creature with a morph ability face down.

Whenever a Beast enters, you may gain 3 life.

Haste T: Turn target face-down creature you control face up. At the beginning of the next end step, sacrifice it.

Double strike (This creature deals both first-strike and regular combat damage.)