Combustion on Holy Caster seems not working. At least it's not increasing number of fireballs shoot by wyrms. I got 2 extra fireballs on it but visually they still shooting only 2 per volley (meant to be 4).
Gonna test it abit later in damage purpose to see if 2 fireballs vs 4 will double the killspeed.. just need get to some stationary boss without minions and shit.