Give the unit a Buff type behaviour and use the Vital Leeched from Damage Dealt property located under the Combat tab in the Behaviour: Modification + property. You can set the amount leeched depending on the type of damage (melee, ranged, spell or splash). A value of 1 means 100% leeched.
I want it to be an ability, like unit hits target for 100 dmg, receiving 50% of the dmg dealt in health. Could I just make a validator that checks if the dmg was dealt by this ability?
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.