Could use a few cards like Withered Wretch or Relic of Progenitus that serve the dual purpose of clearing out enemy graveyards while also letting you exile Kokusho to the command zone after she dies and triggers. The Murderous Cut in your list is a good start.
Sphinx of the Chimes can dump rats into the graveyard faster than you can cast them, and draw crazy amounts of cards, while being a decent Mahamoti Djinn besides.
Eater of the Dead can mill a ton of cards quickly with Phenax while clearing out opposing graveyards in advance of Living Death et al.
I would also add more card drawing and a Demonic Tutor in place of some the redundant effects.
Eternal Dragon has the benefit of being a usable card in the early game and a recurring closer in a slow, locked-out late game. Celestial Colonnade is similar in that it replaces another land in your deck but becomes a real threat in the late game.
All the shuffle effects mean that Sylvan Library is probably a must and Scroll Rack should at least be considered. More card drawing can come from Greater Good because you will often have more 5/3s than you can easily use.
Having a bunch of 5-power creatures get chumped until they can be dealt with is no fun, so I think Nylea, God of the Hunt should be in there and maybe some of your other favorite trample enablers as well.
The new Myriad Landscape both synergizes with Titania as a self-sacrificing land and ramps you to 5 a turn faster. I would also consider Dryad Arbor in the land base because you have 4 fetches that can tutor for it and it's a fine card to have out in case someone Wraths with Titania in play since you get a 5/3 after the carnage.
There's also the possibility of Greenseeker because you'll probably end up in a lot of board states with some basics in the yard and will want recursion. Another small creature to consider is Drumhunter for card-draw and mana each turn.
Corpse Connoisseur is triply good with Sidrisi: it has value if milled, it puts a creature card directly from the library into the grave for a Zombie token, and it serves as another Entomb. And it's even a Zombie.
Also, Forbidden Alchemy as another search option that mills and is useful even if milled.
Maybe there is space for Phenax? Tap Zombies to make more zombies? You might not even need his loyal servant Eater of the Dead.
Also Kozilek reshuffles your whole graveyard, which can be a problem if you have goodies in there (unearth, flashback, Genesis, etc.) Perhaps to enable combo #1 you could use something like Dread instead?
You definitely want cards that can exile Kokusho from your graveyard, so that you can put it back into the command zone after the death trigger. Withered Wretch, Relic of Progenitus, Murderous Cut, etc. My favorite, though might, be Diabolic Servitude. When the reanimated Kokusho dies, it will both trigger *and* exile itself to your command zone, and you get Servitude back into your hand to do it again.
I think I'm going to try to use a Necrotic Ooze based combo as the win condition for mine. Sidisi in this build would be more of an enabler, with her zombies fueling Altar of Dementia and Extractor Demon
The best Necrotic Ooze combo involves Phyrexian Devourer, which if you don't get the Ooze, also lets you mill out an opponent with the Altar of Dementia that is already good in the deck, provided you have enough cards left in your library. (After the Devourer sacrifice ability goes on the stack, you can let it hang there and keep pumping it until you have a big enough Devourer to mill an opponent's entire deck.)
I think the deck really wants Glissa, the Traitor as a way to get back a milled Altar, Basalt Monolith, or Mesmeric Orb, and it incidentally is a great ground blocker that can join in attacks as well.
It's money, but the deck probably wants Personal Tutor almost as much as it wants Mystical Tutor. Especially when you have things like Time Stretch and Razia's Purification available.
Phantasmagorian at 7 mana seems like a great choice: If you have three non-creature cards in your hand, you can simply pitch Phantasmagorian to Volrath then return it to your hand, then pitch it again if that's what you need for a kill shot.
Eater of the Dead can mill a ton of cards quickly with Phenax while clearing out opposing graveyards in advance of Living Death et al.
I would also add more card drawing and a Demonic Tutor in place of some the redundant effects.
Even better, just Tooth and Nail for Kamahl and Masticore together.
There's also good old Drogskol Reaver.
Having a bunch of 5-power creatures get chumped until they can be dealt with is no fun, so I think Nylea, God of the Hunt should be in there and maybe some of your other favorite trample enablers as well.
The new Myriad Landscape both synergizes with Titania as a self-sacrificing land and ramps you to 5 a turn faster. I would also consider Dryad Arbor in the land base because you have 4 fetches that can tutor for it and it's a fine card to have out in case someone Wraths with Titania in play since you get a 5/3 after the carnage.
There's also the possibility of Greenseeker because you'll probably end up in a lot of board states with some basics in the yard and will want recursion. Another small creature to consider is Drumhunter for card-draw and mana each turn.
Also, Forbidden Alchemy as another search option that mills and is useful even if milled.
Maybe there is space for Phenax? Tap Zombies to make more zombies? You might not even need his loyal servant Eater of the Dead.
Also Kozilek reshuffles your whole graveyard, which can be a problem if you have goodies in there (unearth, flashback, Genesis, etc.) Perhaps to enable combo #1 you could use something like Dread instead?
The best Necrotic Ooze combo involves Phyrexian Devourer, which if you don't get the Ooze, also lets you mill out an opponent with the Altar of Dementia that is already good in the deck, provided you have enough cards left in your library. (After the Devourer sacrifice ability goes on the stack, you can let it hang there and keep pumping it until you have a big enough Devourer to mill an opponent's entire deck.)
I think the deck really wants Glissa, the Traitor as a way to get back a milled Altar, Basalt Monolith, or Mesmeric Orb, and it incidentally is a great ground blocker that can join in attacks as well.
Other ideas for expensive cards to get can include Blatant Thievery, Decree of Silence, and Cast Through Time.
Plus it's amazing with the Seedborn and Prophet that you are inevitably playing.
Tradewind Rider: Once a powerhouse in Standard, now often overlooked.