Cow Swarm

Defender, Trample.
Whenever you cast a Cow card, create a 1/3
Green White Cow creature token with trample.
At the beginning of your upkeep, if you
control five or more Cow creature tokens,
sacrifice five Cow creature tokens and create a
copy of this card.
If you control Three or more cows,
this card can attack as though it
doesn't have defender.