MTGO > Commander > Scattering Stroke

Counter target spell. Clash with an opponent. If you win, at the beginning of your next main phase, you may add {X} to your mana pool, where X is that spell's converted mana cost. (Each clashing player reveals the top card of his or her library, then puts that card on the top or bottom. A player wins if his or her card had a higher converted mana cost.)