Helm of the Ghastlord is one that you'll have to add more protection for Neku to have on the field for more than a turn, but wins.

Alright I am here to help! Sorry it took so long but I didn't have any time because when I help out people it usually turns into a wall of text which it is! :3 (Disclaimer: I didn't have time to check for grammar so excuse the mess XP)

Alright I here to help! First Suggestion: You need more pain outlets. Your deck is missing some of the most powerful ones. In this case: Megrim, Liliana's Caress, and Bloodchief Ascension all which bring more damage to the table and relives your need for Nekusar to even be on the field. Megrim and Liliana work well with discard wheels which I noticed your running very little of (which is the next suggestion that is coming up) and Bloodchief Ascension can literately win games with a simple Wheel of Fortune and its requirements are extremely easy to fulfill in EDH and no to mention that the cards you run deal damage as well.

Second suggestion: Add more wheels. The more wheels the merrier with more wheels combo out becomes extremely easy even more so with Waste Not which is why I highly suggest you add more discard wheels if you add my suggestions above and remember redundancy is key. Suggested Wheels: Reforge the Soul - It may be an almost worse Wheel of Fortune but discard wheels are wonderful with Waste Not, Megrim, Liliana's Caress, and Bloodchief Ascension. Whispering Madness - An almost worse version of Windfall but it has the added benefit of being able to be reused via Cipher if you see an opponent open. Sire Of Insanity and Dark Deal are two other suggestions as they also allow you to not rely on Nekusar as much and you can instead ride on the back of Bloodchief, Waste Not, or Megrim/Liliana with a mixed of other things but besides these wheels I also suggest these as well. Molten Psyche - If a opponent has a lot of cards or after chaining wheels this will dealt tons of damage and you seem to have enough artifacts to support this. Time Spiral - Basically a free wheel and allows the chaining of another wheel right after it. Timetwister - I don't know if you can afford it but this wheel is the best non-discard wheel and is part of the P9 for a reason, like Time Spiral they both reshuffle your graveyard into your deck so you can reuse things and avoid drawing yourself out. Otherwise a budget version of this which I am running is Time Reversal which works out pretty well. Now if you don't like the "Time" cycle of wheels because they give your opponents back cards as well that is a minor issue as they still have to find it again and grave hate such as Leyline of the Void can also help against that draw back. However, if you are trying to go for a mill wincon I suggestion you avoid that route simply because it super easy for an opponent to shuffle their graveyard back into their deck in EDH anyway especially with Eldrazi and Elixir of Immortality running around (and if they are not milling people out usually will cause them to add in something like this) and damage is much faster than milling anyway.

Third Suggestion: Remove Howling Mine like effects. Why? because you can't control them and they can't be use to win outright, for example say if you have no pain dealers on the field either because its still early game or opponents removed them (I know I have gone through this many times). Your basically giving your opponents free draw for no cost which makes you more Group Hug at that moment and you do not want to give your opponent any advantage without a price. Which is why I run more wheels because they allow a big burst of damage at once instead of slow damage while at the same time being able to control when opponents get to draw. Howling Mine effects in your deck include: Howling Mine (duh), Forced Fruition - because this effectively allows your opponent to draw anything they will ever need, Kami of the Crescent Moon, Teferi's Puzzle Box - not really a Howling Mine effect but it can really mess up your hands in uncontrollable ways, Font of Mythos, Seizan, Perverter of Truth - He may be a big creature but he still suffers the same problem as the rest not to mention you are also losing 2 life and most five drop creatures will probably out class him in any battle. Master of the Feast - To be honest I am on the fence about this one since it is above the curve in P/T so he could be decent to keep but I would just remove him as well.

Fourth Suggestion: Removal of unnecessary cards. With all this suggestions you would need space to put them somewhere and I just happen to have found some spaces in your deck. Toil / Trouble - target player effects like this one are pretty bad in Multiplayer EDH if you are just looking for card draw add any of the following: Mystic Remora, Underworld Connections, and Phyrexian Arena. Prosperity - Practically strictly worse than a wheel until X is pass seven but with that much mana you could just chain wheels. Cerebral Vortex again you want effects that hit all players because killing someone is usually the sign that everyone else should kill you since Nekusar decks generally have a weak defense. Sensei's Divining Top - I find this card unneeded in Nekusar decks due to all the card draw. Nicol Bolas, Planeswalker - I remember when I had him in here but then I realized he didn't actually help me get any closer to a win and ditch him in favor of furthering my wincon. Jace's Archivist - I use to have him as well but removed him because of lack of haste which turn out to be more game breaking than I originally thought as someone could remove him before he did anything and if I wanted to win that turn I couldn't use him right away so I just replaced him with a wheel. Jace, Memory Adept - You shouldn't go the mill route with Nekusar like I said earlier and the rest of his abilities are meh in EDH. Jace, the Mind Sculptor - He could be fine but usually this Jace attracts more hate then anything else even in competitive environments which is not where you want to be in a deck with lower defenses. Sorin Markov - attracts hate from everyone else on the board if their are still other players alive. Tamiyo, the Moon Sage - Pretty meh imo in Nekusar. Kederekt Parasite - requires other perm that is red which you kind of lack in this deck to be of any use. Distant Memories - because giving your opponents a choice is never a good thing so it would be better for you to just run a tutor in its place. Corrupted Conscience - Everyone who sees Nekusar instantly thinks "OMG only 10 infect damage to win instead of 40? sign me up!". However, I wouldn't recommend it, why? because if you are unable to play another wheel after to rack up to 10 infect damage and you lose the enchantment all that damage you could have done goes to waste as you can no longer deal any more infect damage. It also can get you 2 for 1 by spot removal due to it being an enchantment and everyone will band together to remove that as soon as possible and perhaps fearing you have more infect damage in your deck and all gang up on you and then your dead. You could setup for the infect damage so it won't fall flat on its face but by the time you done that you can already win with regular damage. But if you insist on keeping infect damage in here at least use something like Tainted Strike for the surprise factor and it cost only one but I wouldn't recommend it either.

To sum it all up, I recommend more wheels (especially discard ones) and more pain discard effects. I also believe you should get rid of all Howling Mine effects due to the inability to control them and chain them. Avoid cards that target only one player. Some final suggestions for you are to add in a few more wraths (Cyclonic Rift, Toxic Deluge, and Blasphemous Act are some of the better ones in Nekusar's colors). Add in more mana rocks that cost 2 or less (such as the ones in your sideboard) with the exception of Chromatic Lantern because that one is just amazing because with Nekusar you want to win as soon as possible so the card advantage that you give your opponent doesn't kill you in the end. In the end the most important thing in Nekusar is still go all in and save your counterspells for anything that would stop you from winning or anything game breaking. :3 (which is why I also recommend Snapcaster Mage)