Fun wild deck I made mostly because I opened golden Krul, the unshackled in a pack, so I've decided to put a buncha demons in a deck and see what happens. Honestly, it exceeded my expectations, even though it is not perfectly refined.
Mostly you play your 1-2-3 drops early in the game, then buff'em to get favorable trades, in conjunction with kazakus and removal spells you should get to late game without much difficulty. Don't be afraid to lose a mana crystal if it gives you the board, but be cautious if you are going to discard cards - malchezaar's imp and soulfire are mostly here because they are cheap and effective, not necessarily to synergise with each other. Same goes for voidcaller. Doomguard mostly gets summoned by Krul, ideally in conjunction with Mal'ganis. After that your opponent concedes 90% of the time. Overall, if you have little luck with RNG, try switching those cards with something like Shadow Bolt or Hellfire
Do not play all your big stuff at once unless necessary - the psychological effect on your opponent when suddenly you get a huge board out of nowhere by playing Krul should not be underestimated.
Jaraxxus is here in case you need an emergency heal, but 3/15 body can also work wonders after being summoned by voidcaller.
Finally, while cabal trafficker is a very good card, beware of getting Unlicensed Apothecary out of it, it can royally screw your Krul play.