The increase "its damage by 50%" does that occur after something like maximize spell? How does that work with Empower spell?
Basically my question is, do I add 50% damage after all metamagic feats have been applied and dice have been rolled?
I know some of the mythic rules and abilities are busted, but that seems super busted when combined with something like mythic disintegrate, with 3d6 per CL.
I'd assume it works on the base damage of the spell, same as how an empowered maximized spell maximizes the base damage and then adds 50% of the non-maximized base damage on top of that. So an empowered spell* with channel power applied to it would essentially do double damage (base + 50% of base + 50% of base = base + base). An empowered maximized spell with channel power applied to it would do (max + base) damage. At CL 20, your empowered maximized mythic disintegrate using channel power would do 360 + 60d6 damage on a failed save, which is quite a lot.
*assuming the spell deals solely variable, numeric damage