Just some silly thing i found out in MgT (5 man Sunwell instance)
There are these mobs called Sunblade Blood Knights. (Not sure about Sunblade tho )
Anyways, after you engaged them they will do a Seal of Wrath ( red beams from his feet) : Does additional Holy dmg on attack. Spellsteal it and spam ice lance, dagger him, do anything (yes even polymorph) and you will do between 1200 and 1700 extra dmg, it even critted for 2.4k once.
Also there are Sunblade Magisters there, every time they cast a frostbolt they get extra spellhaste, it keeps stacking and you can keep spellstealing it, i got my Pyro to 1 second with a tank just keeping it shooting on him and not interrupting the frostbolts.
Have fun