Oracle

Instant - Trap 

If an opponent gained life this turn, you may pay B rather than pay this spell's mana cost.
Target player loses 5 life and you gain 5 life.

Tournooi-info

Legal in: Vintage, Legacy, Modern, Commander

Officiele rulings

10/1/2009
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.

10/1/2009
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.

10/1/2009
Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.

10/1/2009
Needlebite Trap’s alternative cost condition checks only whether life was gained. It doesn’t care whether life was also lost. For example, if an opponent gained 4 life and lost 6 life during the turn, that player will have a lower life total than they started the turn with - but you can still cast Needlebite Trap by paying B.

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