2013-07-01 : If the target creature’s toughness is greater than 2 when the ability tries to resolve, the ability won’t resolve and the creature won’t be destroyed.

2013-07-01 : If there are no legal targets available, the ability is simply removed from the stack. If you control the only creature with toughness 2 or less, you must choose it as the target, though you can choose to not destroy it.