Dreaded Thirteenth Spell

Pick 1 enemy unit within 13'' of the caster and
visible to them, and roll 13 dice. For each 4+
that unit suffers 1 mortal wound.
You can then summon 1 unit of Clanrats to the battlefield, and add it to your army.
The summoned unit can have up to 1 model for
each mortal wound that was inflicted by this spell.
The summoned unit must be set up wholly within
13" of the caster and more than 9" from any
enemy units. The summoned unit cannot move in
the following movement phase.