I've just got a new spel idea thanks to Mooboy.
A new talent for shadow priests.
Spirit of Revenge :
Increase total haste by 5% (the stats not the percentage) and upon death, the priest becomes the Spirit of Revenge for 15 sec, The Spirit of Revenge cannot attack, be attacked or targeted by any spells or effects.
While in this form, the Priest can cast "Possess" :
Allows the Priest to Possess a group/raid member for 15 sec and increasing its spell damages by 20 % (so only usable on Mages, Locks, Priests, Sham, Moonkin)
This effect occurs only if the priest dies in Shadowform
(Think of a Spirit of Redemption like spell, we morph into a kind of "I-don't know-what" just after dying in Shadowform during 15sec , we can move and reach the raid member we want to posses -8yard range, once he is, the raid member get a buff "Possessed" with a dark animation, I though of a dark fantomatic form of us behind the possessed one casting at the same time than him/her)
Would be funny ^^