Vorpal Maelstrom

An aetheric whirlpool manifests in the heart of
an enemy formation, snatching up warriors and
smashing them against each other.
If successfully cast, pick a point on the battlefield
within 18" of the caster that is visible to them.
Roll a D6 for each unit within 3" of that point.
If the dice roll for a unit is less than or equal
to the number of models in the unit, that unit
suffers D3 Mortal Wounds.