Champion of the Forest

Trample
Whenever Champion of the Forest attacks,
you may search your library for a green creature
card with converted mana cost less than or equal
to the number of lands you control and
put it on the battlefield tapped and attacking.
At your next end step, if a card named
Arbor of the Champion is in your graveyard,
return the creature found this way to your hand.
Otherwise, exile it.