It really depends. I assume you're talking about Orange demons, but you could use others (crimson has a few, and a couple of the magicians are dual with crimson/pale green).
If you use Orange, work in Wandering Spirit, Spirit of Temptation, Trembling Spirit, and other very useful generic demons. Then put in a Gates of Hell. Wandering Spirit CBN band to Spirit of Temptation CBI band to any of your human magicians (who are mostly CBI) creates some mean combos, and even if they discard you, Wandering Spirit and any other orange demons go to the bottom of your deck, where Gates can bring them out.
Pair that sort of knowledge with your magicians, who can reveal bottom cards to do mean things. Really, the best thing to do is go in the RTS or REG, look at all the demons and magicians and related enhancements, and find what you like and what combos work. Things like Invoking Terror will pop out at you.
It's more fun to find a deck you like yourself, trust me.
(By the way, I've always loved magician/orange demon defenses, they're fun to play at least
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