Caldt, Devourer of Fens

As Caldt, Devourer of Fens enters the battlefield, you may sacrifice any number of lands. For each land sacrificed this way, Caldt enters the battlefield with a +1/+1 counter on it.
Whenever a land is put into the graveyard from anywhere, put a +1/+1 counter on Caldt. Then, you may pay {b}{g}{g}. If you do, return target basic land from your graveyard to your hand.