@PKMNB0Y Err, ok. I've some more suggestions! Also, if you just don't want that power in, do say so, and I'll remove it. Switch it to something of lesser potency.
Left hands: Left hands, aka Hands of Glory, refered to as the left hand of a murderer, or criminal, considered to have evil power, as the devil was the metaphorical left hand of god. While less gore focused, those that knew about the Christian religion, they'd know of what he was doing, and as such those people would react especially badly.
Kills=Power: Naz killing an evil person damns them to his hell, and empowers him, allowing his summoning powers to manifest. This is the least effective per kill, and more easily swallowed by the others, as some may see it as a natural progression, unless they are against condemnation, which would lead them to a conflict with Naz.
Non-Kill reliance: Another route for the power, is to make it so it charges up overtime, and as such, it would make it so he could almost always summon something, but never manage to truly get into the stronger more versatile summons, unless he waits a long time. It would take almost a week to summon a winged imp, a good creature for scouting, but not at all physically or magically powerful.