I have a Magery Mastery Serpentine Dragon with 1,039 INT/1,500 Mana/30 MR/120 Magery/120 Eval. He still does less damage than a Chiv+AI pet, despite being the most powerful spellcaster a pet can be. His Mind Blasts do hit pretty hard though. There's a few bugs with Magery Mastery that really hamstring them too. They cast Bless on their opponent rather than themself. They cast Magic Reflection, which oftentimes means they end up taking more incoming damage. Death Ray is a total waste on them, since it replaces their melee, does less damage than their melee, and is easily interrupted before it can even tick, just sucking down Mana.