Zharrgron Flame-spitter

Summoning: Set up wholly within 6" and visible to chanter, more than 1" from all models and terrain.
Magma Blast: Start of your shooting phase, if
there are any friendly FYRESLAYERS PRIESTS within 6" of this invocation, you can pick 1
enemy unit within 24" of this invocation and roll
12 dice. Add 1 to roll if unit has 10+ models. Add
2 to roll instead if unit has 20+ models. For each
6+, that unit suffers 1 mortal wound. If you roll
a 4 or more unmodified 6s, after mortal wounds