Imbued Jade Stone

Imbued Jade Stone enters the battlefield tapped.
{t}: Add {g}.
Sacrifice Imbued Jade Stone: Add {g}{g}{g}
to your mana pool. When you cast your next
creature spell this turn, create a token that's a
copy of it, except its power and toughness are
each equal to half that creature's power and
toughness, rounded down.