There are also a lot of honorable mentions for demon related cards that are not actually demons themselves. For the most part a lot of these are better than the demons on the actual list!
Skirsdag High Priest is quite brutal in the right circumstances. I would have him about 4th on the list. Better and more playable than most of the demons not in the cube. When he is good he is unreasonably good, making 5/5 fliers for no mana or life cost, just tapping some dorks, is hard to beat. This guy owns most stalemates and he is just a painless two drop. The reason he isn't played loads is that he does so pathetically little when you don't have an excess of guys or ways to get guys dead. Black has actually recently gained some useful cheap utility dorks in Carrier Thrall and Cryptbreaker than should make this card perform better. If you have cheap utility dorks and useful things to do with pointless bodies (such as Recurring Nightmare or equipment) then Skirsdag High Priest is a potent tool, if not he is liable to not do anything.
Promise of Power is a blast from the past! While it offered some utility it was rare to entwine and rarer to be any good at all when just making a token. Five life and five mana for five cards is decent but it is inflexible and not a better tool than Skeletal Scrying, Necropotence, Necrology, Yawgmoth's Agenda or any of the top end alternatives really. As such this saw too little play and was cut never to return many years ago. Investing so much mana into a token that can easily be bounced to death equates to too much risk. Probably better than Grinning Demon or Yokura but not by enough!
Ob Nixilus comes in several shapes and forms. All his creature forms have been too convoluted or pricey to merit cube attention however his planeswalker forms have been far more impressive. Reignited would come in at 3rd on this list and Black Oath only a couple of places below. Reignited is either a Phyrexian Arena or a removal effect as you need which provides a lot of gas and utility and has him as one of the most rounded planeswalker in the game. Black Oath is narrower but dangerously high impact. The ability to have a 5/5 flying demon in play and a planeswalker right away is pretty swingy. The drain life in minor but gains loads of loyalty and life can usually be turned into cards in black decks! Both offer more to your deck than most of the four and five mana demons that are on this list and are widely playable.
I lied, I have not properly tested Priest of the Bloodrite! Given how remarkably close it is to Ob Nixilis of the Black Oath I don't feel I entirely need to. It is better in decks where you have creature synergy, specifically Recurring Nightmare but general sacrifice outlets but potentially flicker effects as well improve the card. Situations where you just need blockers it also outperforms Ob Nixilis of the Black Oath. Without synergies the card is narrower, less powerful, offers less utility and hurts you going forwards rather than aiding you. Given that Black Oath is infrequently played in cube the Priest seems a bit over indulgent although it probably still makes the top ten either directly behind Black Oath or pretty close to there.
Now for the actual demons that are too weak to make a top 10 list......
Sire of Insanity didn't last out the testing phase in cube. He was too high up the curve for the effect and not enough body for the mana. He was utterly brutal for some of the slowest decks but then most six drops should do that and be playable in other places! Cute but weak and really more of a hoser. Scaled down to a four or even five mana card and in only one colour and it might have stood a chance.
Extractor Demon is an interesting cube option. While pretty unplayable if you plan to hard cast him the unearth is great value. In any dredge / discard themed deck Extractor Demon is an interesting option. He also has the ability to further mill you making him both the enabled and the enabler in synergy decks. Sadly far too narrow to include in the main drafting cube but one of the few demons that performs a specific role rather than just being big and demony!
Speaking of just big and demony, Desecration Demon is quite a lot of card for the mana and not the kind of drawback that will wreak you, just one that leads to a bit of a dead do nothing card too much of the time for this to be all that good. Unlike Abyssal Persecutor where the onus is all on you to mitigate the drawback of the card Desecration Demon just depends on what you are up against. Versus control the card is generally just a complete beating but against any sort of weenie or token deck you have a four mana card that will do basically nothing. No blocking, no attacking, just a load of eating plant and soldier tokens or off the top one drops. While this demon can't go rogue as it were and just kill you itself a four mana do nothing card is pretty much the same as killing you. Desecration Demon always seems nice enough when building as you don't have to think about it too much, just a nice good value 6/6 flier for the bargain cost of 4. The issue is when you come to cast it and wish it was an Abyssal Persecutor instead or indeed any creature without a built in Pacifism. The +1/+1 counters may seem like some compensation for the tap drawback but it is basically just being given a tissue to wipe away the blood from the beating you just received, more humiliating than useful or comforting.
Shadowborn Demon had some promise but it turns out six creatures in your bin just never is a thing any time early. This makes Shadowborn pretty niche, you want to be playing it in some dredge style deck or one with loads of recursive stuff like Bloodghast. The real tragedy is how much better Shriekmaw is than this. Certianly the spot removal aspect of this hits a wider range of dorks than Shreikmaw but you can't do it for two. Even when you do them both for five the Shreikmaw has comparable evasion, a not wildly lower amount of power and has no upkeep costs. Cube cards want to be reliable and flexible and not impose things on your deck design. Shadowborn Demon fails at these things pretty hard. At best he is a five mana two for one that comes on a body not exactly above the curve in cube terms. At worst he is a five mana spot removal one for one that also fogs them for a turn. Playable, occasionally good enough, even in the wrong decks but far from broken at its best and way too narrow.
10. Rakshasa Deathdealer
A bit of a jumped up Putrid Leech come Nantuko Shade! Golgari has a wide range of good two drops of which this is one of the less exciting. Its abilities all cost mana to use making it basically a Grisly Bear for most of the early game. Late game it is certainly one of the better two drops you can top deck but a card which shines most as a late game topdeck is not the kind of thing I look for in a cube card. Certainly quite playable but no where near the power level needed for a gold card to be an auto include. Getting much out of this requires having too much spare mana which is not a thing one associates with cheap aggressive monsters. Potentially very powerful but ultimately less effective than Putrid Leech or River Boa!
9. Butcher of the Horde
This guy is really good. Really really good. What he is not is playable. It is so rare to see a Mardu deck in cube that this just never gets played despite being good enough to play in any deck with other creatures in it. The other massive issue for the card is that Falkenrath Aristocrat is just better. The one colour less makes it quite spectacularly more playable. Indestructible is a better effect than any of those offered by Butcher and also makes up a lot for the toughness difference. Further to this having haste without the need to sacrifice a dork more than makes up for the one power difference. When you have a load of disposable tokens and are not facing any removal while also being in Mardu colours the Butcher of the Horde can out perform Falkenrath but this doesn't happen. This is why some cards wildly above the curve just don't see play. Something does their job more conveniently or you just have no place to play it in.
While a 3 mana 5/5 flier is juicy it is a big old risk to give your opponent a Howling Mine. As it is such a threat it is often killed with sorcery speed stuff before the card draw triggers leaving everyone at a fair one for one trade. The blow out it when they have instant effects like tap, bounce, destroy etc where they can get a two for one at your expense. Worse still if they lock it down with a Tamiyo or something. All told the risk is too great for this to be a good standalone card. Fine against some archetypes but a liability against others. Where it does have its uses is when you have enchantment synergy. This can me more than enough to push it over the top. A 3 mana 5/5 flier is a seriously powerful card. If you can trigger enough things with it being an enchantment then it doesn't matter if you go zero for one with it to instant removal. Alternatively you can just play if off the back of a mana elf on turn two where it has so much tempo that any card disadvantage you give away is negligible as the game will be done too quickly for it to matter. In this regard there is a lot of comparison to Goblin Guide. Sadly green black doesn't quite have the same finishing power as red with its burn to pull of the same kind of strategies.
7. Overseer of the Damned
At seven mana this is a little outside the realms of the commonly cast cards. It is the sort of thing midrange decks love, a well rounded card with no drawbacks and value all over the shop. If it were scaled down and made a five or six drop it would be a cube mainstay. If you are actually going to the effort of hard casting a seven drop you don't just want good value you want something that ends games. In reality this has a bit of a 4 turn clock and only affords ongoing value if you have more removal. As a reanimate target it is a little too fair. It offers a slow clock and only gives value if they have things to kill. Typically you are better of with proactive cards not reactive cards for recursion effects. His best home is a Golgari Recurring Nightmare style deck where you have ramp and discard outlets to stop him being a liability in your hand. Certainly viable for cube but not played as much as the quality of the card suggests. Sheoldred is more exciting as top end goes, Grave Titan packs a lot more punch for the mana and things like Shriekmaw and Kalitas are far more preferable in any sort of midrange affair simply because they are relevant in the game that much sooner.
6. Bloodgift Demon
This is the all rounder of the group. It is a decent enough body for the mana and has the promise of value should it not be dealt with right away. It even has a rare get out of jail effect built in which allows you to direct the life loss and card draw towards your opponent. Not ideal but at least it means you are hitting for 6 over 5. In many ways Bloodgift Demon is an amalgamation of the best modes from both the 5 mana Ob Nixilus planeswalkers. He is a big flier than costs you some life and he does a bit of Phyrexian Arena for you too. A great limited card but a bit vulnerable to removal to make a lot of the more streamlined decks. Planeswalkers tend to get more immediate value regardless and are generally harder and costlier to kill with removal. There is still a lot to be said for a big fat flier in cube and this is one of those that works in most places.
5. Herald of Torment
The black Boon Satyr (kind of). Herald of Torment is a nice rounded little card that is far more playable on the cheap end than Boon Satyr and far easier to engineer playing as an aura as well. While it is never a combat trick it is a significant threat. When you bestow anything with Herald you end up with effectively a massive evasive haste threat and utterly break any stalemates. Then, they are in a rush to deal with the dork you bestowed which will usually get in enough damage that the 3/3 flying leftover you get is also a serious threat as well. The enchantment aspect of the card allows for it to work fine in some synergy decks but for general use it just makes it a bit easier to deal with. The lifeloss is negligible most of the time but forces you to play and build with it in a certain way that does leave it a tiny bit on the narrow side. Certainly a card of sufficient power to be in cubes but fighting with a lot of top rate three drops for a slot.
4. Daxos's Torment
Speaking of enchantment synergies we have this somewhat demon card. This is one of the best threats in the game if you are able to reliably trigger it. Thundermaw Hellkite is one of the best threat in the game and it costs a mana more and dies to far more sorcery speed removal. There are some decks you can play this in and it is truely outstanding. The issue is that you can't draft those kinds of deck as no sensibly balanced drafting cube will contain enough of the weak enchantment support cards you need. In the more constructed style cube things however this card is all sorts of powerful and interesting. Not only is a four mana 5/5 semi-hexproof flying haste but it has no painful or sacrificial drawback that you would normally expect from an above curve black card. This is absolutely a potential sleeper for if we ever go back to Theros and reach a critical mass of playable black enchantments. Most of the demons on this list have gotten worse over time but this one should do the opposite.
3. Abyssal Persecutor
Despite not being such a main feature anymore this big dork had a few years where he was one of the biggest names in cube. I still have him in my cube and he still sees enough play to retain his slot. These days he is not so far above the curve in power level that it is that worth it making your deck suitable for him, you just play him when your deck happens to ork with him (ie have ways to remove him from play). He is just a nice efficient threat and generally you don't want those making your life difficult. There are several reasons Persecutor is all sorts of good. Firstly he is comfortably 6 manas worth of body and secondly his drawback is more often than not completely blank text. The general rule is that either your opponent kills the Persecutor for you or it kills them. You do sensibly need answers to it or sac outlets for it yourself but these are relatively easy to pick up and include. Even if you don't have one to hand your opponent has to respect that you might well have one and will likely draw one in enough time. Sometimes it will put them to 0 or less and you have to wait a little to draw your removal but I have only ever seen the drawback cost one game in hundreds. The thing is, when you get someone to 0 most of the time you don't have to attack more. A 6/6 flying blocker that you can't remove in anyway really does make winning hard. Abyssal Persecutor is still one of the best outright beaty threats on offer. It hits really hard and really reliably while being a bugger to remove. It is not that better four drops are on offer it is just that a lot of the outright midrange threats have moved to the three slot with the four drop and up being more value cards and more robust things.
2. Ormendahl, the Profane Prince
The most recent demon to grace the cube and it is quite the unusual one given that it starts life as a land. What I have come to appreciate about Ormendahl is the incredible power he can bring to even the most meek of decks. Most of the decks that consider including colourless manlands like Mishra's Factory are those that have a high count of small dorks. In such decks you are essentially taking a tiny consistency hit on your mana base for the chance to eek out a few free damage in floods and late game situations. Usually when you are using man lands in aggressive decks you are losing, not always but more often than not. For the control decks it tends to be the other way round that when they start activating their man lands you have probably lost. Playing Mishra's Factory in something like RDW might cost your good and average draws a small fraction of a % (total stab in the dark but we will call it 0.2%) in exchange for a slight improvement to your weaker draws. You are generally best off aiming for good draws more of the time than trying to make things better when it doesn't happen. You should be hoping to have a favourable win % with your deck. Although far too big, for the sake of argument lets say you are 60 to 40 to win with your aggressive red deck across the board. An improvement made to your losing draws will only be in affect 40% of the time while improving your winning ones will be in affect 60% of the time. Same logic as to why post sideboard matchups are more important for all decks that don't go to time on the round. If you can tip the balance of the scale either side by an arbitrary 10% then you get a value of 6 by improving your strengths and only a value of 4 from your weaknesses. Mishra's Factory is still a fine card and has plenty of application but it is far from an auto include in aggro lists, even mono coloured ones (apart from the fact there are often other better colourless lands options on offer). I have made it sound far weaker than it is by exaggerating the numbers significantly to make them neat.
Now, along comes Ormendahl, he has the exact same cost to inclusion as a Mishra's Factory or Mutavault or Blinkmoth Nexus and as such he has a comparable effect to your top end win percentages. The difference is that he has a vast impact on games unlike the smaller man lands. The odd extra damage or body from the man lands is a mild help that happens fairly often and is relevant fairly infrequently. Ormendahl occurs fairly infrequently but is hugely significant when he does. Ormendahl actually turns losses into wins, something other man lands do a lot less often. It is not just unfavourable situations he can get wins out of but ones where you would simply concede if you had a Mishra's Factory in your deck instead of Ormendalh. He attacks on so many different fronts and is so powerful that he just adds a whole different dimension to any deck that can support him. Green ramp decks and weenie creatures decks are the best place for him but I frequently see him getting put into midrange and control lists. While the token generation aspect of Westvale Abbey is incredibly weak is does allow you to justify playing Ormendalh in decks with lighter creature counts. Both incredibly hard to remove and to race Ormandahl gives a lot of decks a lot of reach they couldn't otherwise justify playing. Lack of trample keeps Ormendahl from being a bit silly, it gives you a bit of time chump blocking to find an answer that it now unlikely to be damage related in any way! If Ormendalh had trample flipping him would mean winning the game the following turn far too reliably. He is pretty impressive in his odds for doing that as it stands anyway.
No shock here that the most played demon in any format is the best cube demon as well. This is the card you most want for most of your cheat stuff in decks. He works with basically all the mechanics bar those that find a green dork and he instantly gives you near infinite gas. Further to this he provides a wall near impossible to attack into and then a threat that is near impossible to race. While it doesn't happen often Griselbrand is even hardcast in the cube. If you have the mana then a threat plus cards is what you want most of the time. I am really quite glad that his card draw has to happen in chunks of seven rather than being a direct copy of Yawgmoth's Bargain. Griselbrand is already pretty much the complete package when it comes to a fat dork. Having to draw cards in painful lumps of seven makes for a much more interesting card.