Buy @ TCGplayer
First strike
{T}: Destroy target artifact if its mana value is equal to the amount of unspent mana you have.
The artifact’s converted mana cost must be exactly equal to the amount of mana in your mana pool when the ability resolves. If there’s less mana or more mana, the artifact won’t be destroyed.
The mana has to be in your mana pool before the ability resolves. The ability doesn’t allow you to activate mana abilities while it’s resolving.
