Make some sort of AE spell, like Thunder Clap, and then pick every unit around the caster, create a dummy with a no cooldown/cast/mana Roots, and then check if they have the buff of thunder, most likely tweaked, and then... you.... uhhh.... get the entangle with a Unit- Issue Order targeting an object
Ahh... there is a spell in the spell section. Search for it a little. It is called Mass Entagling Roots or something and it does what you actually required I think.
