I'm not sure what format this is intended for so I'm sorry if any of my suggestions aren't legal. Most decks aiming for big demons opt for reanimation over other turbo out options, but I think you can make it work for a casual deck. I like Quicksilver Amulet for instance and I think you could also consider Heartless Summoning, Ancient Cellarspawn, or Crypt Ghast. Nykthos, Shrine to Nyx makes Coffers slightly worse but I can't imagine it being a bad inclusion with so many black pips. Another option would be to include more demons in the low mana range so that you have some board presence early. Some that came to mind are Varragoth, Bloodsky Sire for tutoring, Master of the Feast if you want to lean into a Underworld Dreams/Orcish BowmastersGC plan, Desecration Demon for stats and potential board denial, and Nightmare Shepherd for removal insulation. Really though, if you want more consistency, the best thing you can do is add more copies of your best cards. This does incentivize picking a clear direction and you don't want to consolidate too much here lest you get too low on unique names for Contract. If I was building this, I think I'd go to 4 copies of Spawn of Mayhem and 2-4 The Speed Demon with a focus on dealing damage or life loss to get their relevant triggers. Changeling Outcast is perfect for this so I'd up them too. Removal like Smallpox or the safer Geth's Verdict can incur life loss, and I do recommend upgrading from Sorin's Thirst and Cremate anyway. Fatal Push, Dismember, and Feed the Swarm are all options with varying strengths and weaknesses. That's just one direction too. You could just as easily build around foretell with Dream Devourer and some symmetry-breaking Damnations, Rite of Consumption effects with overstatted guys like Abyssal Persecutor, or pure devotion with Gray Merchant and Bloodletter alongside tools like The Meathook Massacre or Leyline of the Void. If you pick the handful of demons you enjoy playing the most and run more copies, you'll have more games actually playing with them and can save your tutors for emergencies more often.

Not a deathtoucher, but Kitesail Freebooter does have flying and can keep your opponent off their best card, at least for a while. Assassin Initiate and Covert Cutpurse  ^Flip will do the job but at a steep mana cost. I'd personally like to have a sac outlet more repeatable than Village Rites to recycle Bloodsoaked Champion for more lifedrain and Xathrid triggers, especially during a board stall. Carrion Feeder would be my first choice as a beater that can get out of hand while also sticking to the zombie them. Keeping it to only humans, Dockside Chef is also an option. Speaking of zombie beaters, Champion of the Perished is also potentially powerful, although, like many cards already in the deck, it makes a lot less sense when you don't draw a Necromancer.