Unseen Strike Data actually tells you exactly what he does.
- The buff lasts 5secs and "every 5secs" (which is essentially just once at the end of the duration) he'll inflict
this spell (note it requires Melee Range), which inflicts damage according to the difficulty and causes a knockback
- He increases his runspeed by 200%
- He triggers
this spell, which causes him to fixate on a target
- He triggers
this spell, which causes his invisibiltiy level to increase (by 10.000, for comparision: The mage talent
Greater Invisibility causes invisbility to increase by 340 and
Invisibility Potion grants 200)
What'd be interesting is what happens if you'd time Transendence (Monk), Blink (Mage), Demonic Circle / Gateway (Warlock) or Shadowstep (Rogue) so that his 5s buff expires and he's out of range of his target... Maybe I'll give that a few shots in my alt raid