Ozomatli, Covetous Warchief

Buyback {4} (You may pay an additional {4} as you
cast this spell. If you do, put this card into your hand
as it resolves.)
When you cast this spell, if the buyback cost was
paid, gain control of target artifact until end of
turn. Untap that artifact. It gains haste until end
of turn. Sacrifice it at the beginning of the next
end step and create X Treasure tokens, where X
is that artifact's mana value.