The first one, obviously, is Improved Succubus, which has been modified in the Wrath Beta to confer up to a 100% resistance to interruption caused by damage while channeling Seduction. Succubi have four basic abilities, although they are famous this one alone. If a Succubus is ever brought out for PvP, it is purely for Seduction. They are the easiest demon to kill next to an Imp out of Phase Shift and thus almost never see Arena or even Battleground play. However, Succubi provide invaluable crowd control for humanoid-heavy instances. It helps to use an AddOn like FocusFrame to keep an eye on the Succubus' target because learning to reapply Seduction -- try to key bind it -- is crucial to keeping her alive.