Action: Pick every unit matching: Unit has a buff: Entangling vines (pause), and do: set life of picked unit: current life of picked unit - 15 (or any value u see fit)
Wate, if you do this, any units this spell kills won't give the caster credit because when you take away life threw triggers it doesn't know who is doing the damage. This can be bad in AoS type maps where getting a kill is vital to earn gold or get credit for killing an enimy hero.
The best way to get around this is to create a unit with a damageing spell and is owned by the caster, hide the unit and have it cast the spell.
