Mindbreak Trap

Instant — Trap

If an opponent cast three or more spells this turn, you may pay rather than pay this spell's mana cost.
Exile any number of target spells.

2009-10-01:
You may ignore a Trap’s alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
2009-10-01:
Casting a Trap by paying its alternative cost doesn’t change its mana cost or converted mana cost. The only difference is the cost you actually pay.
2009-10-01:
Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.
2009-10-01:
Mindbreak Trap’s alternative cost condition checks whether an opponent cast three or more spells this turn, not whether those spells have resolved.
2009-10-01:
If a spell is exiled, it’s removed from the stack and thus will not resolve. The spell isn’t countered; it just no longer exists. This works on spells that can’t be countered, such as Terra Stomper.