Burning Simoom

Burning Simoom has a casting value of 6.
If successfully cast, pick 1 enemy unit within
12" of the caster that is visible to them and
roll a number of dice equal to the number of
models in that unit. For each 6, that unit suffers
1 mortal wound. If the casting roll was 10 or
more, that unit suffers 1 mortal wound for each
5+ instead of each 6.