2009-10-01 : Casting a Trap by paying its alternative cost doesn’t change its mana cost or mana value. 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 : You can target any two creatures, not just ones that entered the battlefield this turn.

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 : You must target two creatures as you cast Whiplash Trap. If you can’t (because just one creature is on the battlefield, perhaps), you can’t cast the spell.