I was refering to the mana drain ('Spiritual energy continues to flow into you from a tiger') but I think I made a mistake: it may be not a skill but some special effect from an item:

'Thin black mist seeps from the empty sockets of the skull adorning Abomination, Axe of the Black Serpent, moving to engulf a tiger!
You begin siphoning the soul of a tiger into yourself.'

Seems like the skull adorning Abomination (a part of the Axe of the Black Serpent?) might be responsable for the mana drain.

Just wonder how orcs do it because combined with spinebreaker, it seems quite effective against shifters.