Mana Drain

Oracle Text

Counter target spell. At the beginning of your next main phase, add an amount of C to your mana pool equal to that spell's converted mana cost.

Card Rulings

11/17/2017 Mana Drain can target a spell that can’t be countered. When Mana Drain resolves, that spell won’t be countered, but you’ll still add mana to your mana pool at the beginning of your next main phase.
11/17/2017 If the target spell is an illegal target when Mana Drain tries to resolve, it will be countered and none of its effects will happen. You won’t get any mana.
11/17/2017 Mana Drain’s delayed triggered ability will usually trigger at the beginning of your precombat main phase. However, if you cast Mana Drain during your precombat main phase or during your combat phase, its delayed triggered ability will trigger at the beginning of that turn’s postcombat main phase.