Gengar

Flying, Shadow
When Gengar enters the battlefield, it becomes
Night. When it is Night, creatures you control
have Shroud and Swampwalk.
When it is Day, other creatures you control have
Deathtouch and Toxic 1.
When Gengar does damage to a player, that
player receives an Emblem with: "Lands you
control are Swamps in addition to their other
types.
Mutate {5}{b}{b}{b}{p/b}