The Haunt of Crimea

Whenever a nontoken creature enters the battlefield
under your control put a ghostform counter on it.
It gains "When this creature dies or is put into exile,
return it to its owner's hand and create a 1/1 white
Spirit creature token with flying."
Spirit creatures entering the battlefield under your
control enter with a decayed counter. (A creature
with decayed can't block. When it attacks, sacrifice
it at end of combat.)