Oracle Text

GG, T: Tracker deals damage equal to its power to target creature. That creature deals damage equal to its power to Tracker.

Card Rulings

10/4/2004 Giving either creature first strike does not affect the ability.
10/4/2004 If this leaves the battlefield before its activated ability resolves, it will still deal damage to the targeted creature. On the other hand, if the targeted creature leaves the battlefield before the ability resolves, the ability won’t resolve and no damage will be dealt.
10/1/2009 You may have Tracker target itself with its own ability. If you do, Tracker will deal damage to itself equal to its power, then immediately do it again.