Bueno es un bug viejo pero es impresionante la cantidad de priest que se abusan de esto. La cuestion es que despues de tirar mana burn a un target con psychic scream automaticamente este se tiene que romper, pero aca no lo hace. Entonces si tienen el buff de haste te castean hasta 3 mana burn en un solo fear.

Notas de wowwiki:
* Mana Burn will destroy 10% of the target's mana. If the actual amount is greater than 20% of your maximum mana, it will destroy only an amount of 20% of your maximum mana. This is necessary to prevent Mana Burn from destroying too much mana on enemies with a very large mana pool.
* Mana Burn will instantly break Fear, Hex and Psychic Scream.
* Mana Burn has some strange behaviour in combination with the Shadow tree. It works with Shadow Weaving, Shadowform, Vampiric Embrace, and Vampiric Touch. It does benefit from Darkness and Shadow Affinity. Shadow Focus probably does not affect it, though.
* Its threat simply depends on its damage and follows normal rules; the mana drain does not cause any additional threat.
* Shadowform will increase damage done by this spell.


Fuente: Mana Burn - WoWWiki - Your guide to the World of Warcraft