Vant'athalid, Who Devours

If this card was cast from the Command Zone,
put it into your graveyard instead.
Whenever a creature you control attacks, you
may sacrifice it and put this card onto the
battlefield tapped and attacking. If you do,
Vant'athalid enters the battlefield as a copy of
that creature and gains +X/+X until end of turn,
where X is the sacrificed card's converted mana
cost.