Treason Of Tzeentch

Treason of Tzeentch has a casting value of 5. If successfully cast, pick 1 enemy unit within 18"
of the caster and visible to them. Roll a number
of dice equal to the number of models in that
unit. For each 6, that unit suffers 1 mortal
wound. If any models from that unit are slain
by this spell, subtract 1 from hit rolls for attacks
made by that unit until your next hero phase.