Spiral Overflow

As an additional cost to cast this spell, tap any
number of creatuers you control.
For each creature tapped with this spell, add X
amount of mana in any combination of colors,
where X is the total amount of Spiral Counters
on those creatures.
Buyback {4}{g}(You may pay an additional
{4}{g} as you cast this spell. If you do, put this
card into your hand as it resolves.)