Cobra Trap

Text:

If a noncreature permanent under your control was destroyed this turn by a spell or ability an opponent controlled, you may pay rather than pay this spell's mana cost.
Create four 1/1 green Snake creature tokens.

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 A spell or ability destroys a permanent only if that spell or ability specifically contains the word “destroy” in its text. If a spell or ability an opponent controls exiles a noncreature permanent you control, causes you to sacrifice a noncreature permanent, removes all loyalty counters from a planeswalker you control, or causes an ability you control to trigger (and then that ability destroys a permanent you control), Cobra Trap’s alternative cost condition hasn’t been met.