Kilsbergen Hollow

Kilsbergen Hollow enters the battlefield tapped, and does not untap during your untap step.
Whenever you cast a creature spell, put a seed counter on Kilsbergen Hollow and untap it.
{g},{t}: Remove X seed counters from Kilsbergen Hollow and put a creature card from your hand into play, where X is that card's converted mana cost.
{t}: (Add {g} to your mana pool.)