Darksteel Tide

Whenever you cast a non-creature spell,
proliferate. (You choose any number of permanents
and/or players with counters on them, then give each
another counter of a kind already there.)
At the beginning of your upkeep, you may put a
charge counter on Darksteel Tide.
When Darksteel Tide has twenty or more charge
counters on it, you may cast spells from your hand
without paying their mana cost.