This is a deceptively simple yet powerful trick. Basically, you
1) Get cursed by something.
2) Go into arena or whatever.
3) As you are about to start your burst and enter combat,
remove the curse, and get a 5% damage boost.
The specific curse in the video I I found from this (criminally underrated) thread started by Traxex84:
http://www.ownedcore.com/forums/worl...uff-arena.html (5% damage buff in arena.)