Ideas:

Cinderhaze Wretch
Liliana of the Veil (as if)
Infernal Plunge
Talisman of Indulgence? (use with Oxidda Daredevil)

Some kind of anti-sideboard answer - this deck'll be awesome game 1 and way less good game 2-3 once everyone sides in graveyard hate.  Creature hate is less of a problem since the combo works at instant speed and relies on sacrifice rather than offence or another ability.  Linvala might be an issue.  Counterspells might be avoidable via Cavern of Souls or Aether Vial if I can scrape together the resources to get my hands on some.  Enchantment destruction is likely a must, but really hard; red/black doesn't do anti-enchantment stuff at all.  I really don't fancy splashing green or white just to get a way to kill Rest in Peace or Leyline of the Void.

The other possibility is a transformational sideboard.  Kiki-Jiki is a perfectly adequate win condition by himself.  If I have to splash (say) white for enchantment/arbitrary-permanent destruction, I might as well throw in some Village Bell-Ringers in the sideboard and go infinite that way, although I'll have to take Heartless Summoning out for them to be able to attack for damage.  Splashing green might be more practical anyway though, since it lets me use stuff like Grisly Salvage to fill my graveyard with bullshit combo material.

Super-theoretically, I could actually take red out of the deck altogether.  It's not a great option, since I lose the ability to summon the combo pieces and dump them into the graveyard that way (Mogg Fanatic can kill itself, Crimson Mage dies to Heartless Summoning and Kiki-Jiki dies to my opponent, Lightning Bolt, or another Kiki-Jiki).  It also prevents me from utilising haste, although if I want to expend a lot of resources I can use Aether Vials for that.  I can avoid using Mogg Fanatic by playing Cinderhaze Wretch instead if needs be - the Cinderhaze can be summoned and commit suicide by -1/-1ing itself to death - but the combo is vastly weaker that way, since it relies on attacking.

Wait!  Death Cultist!  It can't kill creatures, but that doesn't really matter.  It also causes life loss instead of damage, which circumvents a couple of really obscure edge cases (Worship, Elderscale Wurm), and the far less obscure edge case of Safe Passage-type spells.  Better yet, I already have a playset.  Win.  And if it fails anyway, at least I have infinite life...

Running green would also allow me to sideboard neat tricks like Ranger's Guile or Withstand Death as pseudo-counterspells to protect my haste-less Oozes.  Then again, there must be some black instant (or activated-ability creature) that gives haste, right?  Skithiryx, for instance.  Skithiryx would be quite a nice alternative win condition actually; he can land on turn 3 off a Heartless Summoning as a giant freakin' bullseye, and when my opponent throws a kill spell at him, I can follow up with a hasty Necrotic Ooze and win.  That'll carry a pretty hefty black mana requirement, though.  The nicest thing is that Skithiryx also has a regenerate ability *just in case*.  Unlike Kiki-Jiki, I don't necessarily *need* to discard him, as my opponent will probably try and shoot him, since he's a regenerating unhealable four-turn clock (three if I blow up my own Heartless Summoning at some point).  It might be wise to have a sacrifice outlet or similar on hand just in case.  Smallpox?  Smallpox lets me sacrifice Skithiryx, discard KJ, and annoy my opponent all at the same time.  It too has a horrid mana requirement, but it's funny.

Cinderhaze Wretch is actually a pretty useful card.  I can tap it to discard KJ or Skithiryx, make it commit suicide (including another discard if I haven't drawn a Heartless Summoning), and spin up the combo.  I can play it on the third turn and an Ooze + haste on the fourth, which'll win me the game either by way of attacking or by Death Cultist life drain, and I can eat my opponent's hand in the process.  That way, I only need to discard one other card, presumably on the first turn via a Faithless Looting or whatever.  I should try and find more one-drop discard outlets in green, black, and/or colourless.  Of course, Delirium Skeins is just as good at being a turn 3 discard everything type card, and hits my opponent to boot, as well as freeing up my turn 1 slot for something useful (mana elf? bolt? inquisition? looting?...)

Hm.  If I'm going green-black I should think about taking Deathrite Shaman.  It's a fantastic one-drop and lets me ramp mana off graveyarded lands as well as hate other people's graveyards.  It even survives Heartless Summoning.

Do I even need Heartless Summoning, tbh?  Turn 3 kills are implausible without mana boosting, and I can do a turn 3 kill with Infernal Plunge without needing it, I think:
turn 1 Death Cultist
turn 2 Faithless Looting, discard KJ + Crimson Mage
turn 3 Infernal Plunge to kill Death Cultist, spend RRBB on Ooze, spend R on haste, win.

So... Infernal Plunge, anyone?

Other haste options:
- Oxidda Daredevil (Sacrifice an artifact)
- Rage Weaver ({2})

Card drawing sounds necessary, too...
- Sign in Blood
- Wild Guess
- Altar's Reap
- Dangerous Wager
- Reforge the Soul???

...or tutoring?  I probably only need to tutor up creatures.
- Birthing Pod + the appropriate mana curve
- Diabolic Tutor
- Jarad's Orders, if I splash or run green
- Green Sun's Zenith likewise

Actually, Aether Vial + Surge Node + Oxidda Daredevil work well.  I can eat the Node (or even the Vial) to give the Ooze haste for a nice turn three kill:
turn 1: Aether Vial
turn 2: pump Vial, play Surge Node, use it to pump Vial, use Vial to play Oxidda Daredevil
turn 3: pump Vial twice, play Necrotic Ooze.  I have two mana with which to kill the Oxidda Daredevil and dump Death Cultist and Kiki-Jiki into the graveyard.  Not that great.  Alternately, I can play the Death Cultist on turn 2 before pumping the Vial, then cast a discard spell on t3 to dump the Daredevil and KJ.  That's a *much* better idea.  Faithless Looting works, or Zombie Infestation.

Hmmmm... not sure how viable this one is.  The main upside of the Aether Vial strategy is that it frees up my turn 3 and turn 4 mana for drawing/discarding shenanigans.  I can flash in the Necrotic Ooze at the end of my opponent's turn to give it fake haste, and then I only need two other cards.  Vial also ticks up by itself fairly well and I can swap in some Volt Charges or similar as Surge Node alternatives.  The key is to get the Vial down on the first turn.

Thinking about Birthing Pod is interesting.  A Pod can curve Oxidda Daredevil into Priest of Urabrask/Avatar of Discord/Geralf's Messenger into Necrotic Ooze by itself.  It can even then turn the Ooze into KJ if I need to pull him out of my library, at which point I presumably sac him to something and summon another Ooze manually, but that's a faff.  Hmm.  Pod does sound like it'll be too slow, but tutoring is good... Podding Daredevil > Avatar > Ooze is a pretty reliable turn 6 win (4-5 with ramp to get the pod out faster).  Avatar of Discord lets me pitch KJ into the graveyard, and the Ooze can use the Oxidda Daredevil's ability to eat the Pod and gain haste that way.  It's tempting to give it a shot; most notably, if I'm tutoring a lot, I can get away with only 1-2 Kiki-Jikis.  Jarad's Orders fits naturally into this deck as a turn 4/5 play alongside Podding up the Avatar of Discord, and I can use it to tutor one card directly into the 'yard and another into my hand that gets pitched to the Avatar.

Hmmmm.  It's a little slow, but sounds quite reliable - there's loads of room for interaction - and only needs five or six cards (four Pods, 1-2 Avatars) alongside the stuff I'm already using.  I'll need extra artifacts to fuel the Oxidda Daredevils though, unless I'm using Crimson Mage instead.  I might as well, actually, since I'll be sitting on somewhere around five mana the turn I play Ooze and the thing will only cost me one or two.  Excellent.

Huh.  I don't know why I only just realised this, but Crimson Mage doesn't actually need to be dead... oooh, that makes life a *lot* easier, since I don't care whether he's on-field or in the graveyard.  Given that Death Cultist can kill himself, all I need to explicitly discard is KJ.  That takes some pressure off.

The Birthing Pod edition might look like this...
turn 1 Arbor Elf
turn 2 Birthing Pod
turn 3 Crimson Mage -> Pod up Avatar -> Discard KJ & Cultist
turn 4 Jarad's Orders if necessary, Pod up Ooze, win

...or
turn 1 Arbor Elf
turn 2 Birthing Pod
turn 3 Pod up Crimson Mage, summon Avatar of Discord/cast Faithless Looting
turn 4 Pod up Priest of Urabrask for mana, summon Necrotic Ooze, win - or summon Priest of Urabrask, pod up Ooze, win
...oooh that one's not at all bad - even if I don't draw an Ooze by turn 4 I can just pod it up on turn 5... and that leaves space for Jarad's Orders on turn four.  This might be the best and most resilient curve yet, since it has lots of redundancy - I can include extra mana elves, extra discard cards, etc.  It also ought to coexist alongside the Infernal Plunge turn 3 curve.

Apostle's Blessing ought to be a nice anti-removal protective card, and Noxious Revival allows second chances as well as being useful hate against Gifts Ungiven or whatever.