Text (TS): {3},{Tap}: Tap target creature you control and target creature of an opponent's choice he or she controls. Each of those creatures deals damage equal to its power to the other.
If either creature leaves play before it resolves, the remaining creature becomes tapped and no damage is dealt. [Time Spiral FAQ 2006/08/30]
Either or both creatures can be tapped prior to using the ability and it still works. [bethmo 1995/08/24]
Creatures with Defender can fight in the Arena. [D'Angelo 2006/10/08]
Blocking abilities like the Thicket Basilisk's do not take effect. [Peterson 1994/11/15]
The power of the creatures when the effect resolves is used to determine how much damage is done. [Aahz 1995/03/07]