Alien's Birth

{1}{b} As an additional cost to this ability, sacrifice a nontoken creature, create 2 1/1 purple alien creature tokens.
{b}{b} As an additional cost to this ability, sacrifice a creature, create a 1/1 purple alien creature token.
Whenever a creature you control dies that was not sacrificed or created by Alien's Birth, create a 1/1 alien creature token.