You need:
-succubus
-grimiore of Lash of pain max rank
-grimoire of Soothing Kiss max rank, too.
-seduction (but you dont have to get it, its only for friendly targets).

Learn all grimoires. Ok, target your enemy, and:
1)RIGHT click on Lash of Pain
2)RIGHT click on Soothing kiss
3)LEFT click on Lash of pain

Now, you succy go to enemy and attack his like 100 damage per second from lash of pain On other servers, succy can unlimited attack from that exploit, because her mana is very fast regen .
Tested on 3.0.3, 3.0.8 and 2.4.3


If you want attack friendly target (only players, because on npc them HP is fast regened), use Seduction on his as first then follow steps 1, 2 and 3