love the demon aspect of the deck , and i may not be the best person for advice on this deck, simply because i don't pay modern. It's just because i started playing when innistrad came out so im not very familiar with many older cards. Only thing i do see a little out of place are the things that produce red mana for you, why are those necessary? Also maybe use some kill spells, instead of using your creatures as the kill spell themselves sometime an outright instant will do better, like Go for the Throat , Tragic Slip , Bone Splinters , or Murder would do nicely.
I use the red mana pieces such as the Rakdos Signet and Rakdos Carnarium s as mana ramping tools so I can get the demons out earlier. The carnariums are also too bounce lands when Ob Nixilis, the Fallen is on the field to boost him and reduce life. Its only a modern deck because me and my friends basically play with whatever cards we have. I have it as creature removal because a lot of the demons or other cards like card:Altar's Reap need a body to make them work. I keep going back and forth on the kill spells. My friends are still using Mirran Crusader to haunt me, but Reiver Demon and the Gatekeeper of Malakir help to kill them while the kill spells would not. Liliana of the Dark Realms is more removal with her -3 as well. This is the deck I always love to go back and work on, I'll try some of your suggestions and see how they work. Thanks!
check out my decks Curse of Time and deck:faster-black-cat-kill-killmaybe cut a few creatures for some kill spells. I can see this deck having a hard time with control right now.. Fun idea though:) Keep it up, I'm sure it will get there!
I'll check back to see your changes