MTG Salvation

This here be my Sidisi list. I've been working on it since Sidisi got spoiled and I'm pretty close to being finished with the list. However, there are a few things I'm still unsure about, so I could use some pointers and suggestions. All kinds of feedback are much loved. Of note is that this IS a RL deck, and while my budget isn't particulary tight, I do not have the cash to shell out for ABUR duals or (sadly) fetches at the moment.

The deck:



Currently on the To-Be-Obtained list:
Mesmeric Orb (Basalt Monolith and Aphetto Alchemist are already here, ready to go in with the Orb. Might do a Morphling as well, to get infinite Morphling-Fatestitcher untap shenanigans)
Filth will probably replace Ghoultree somewhere along the line.
Gravespawn Sovereign. I initially missed this card. Thanks to Wildfire393 for suggesting it.
Tombstone Stairwell. It can do work, I'm sure, I'm just not too sure just how good it will be exactly. Worth testing.

So, how does the deck work? It follows a same pattern the first few turns. Set up 4 mana, cast Sidisi. From that point on, the game goes wide open depending on what gets sent to the graveyard. But the deck has a lot of angles of attack, namely:

Bestow Sidisi with Nighthowler. This can often one-shot a player who did not see it coming.
Mass armies of flying tokens courtesy of Wonder. Sometimes Spider Spawning or Empty the Pits ensure a finisher there.
Mill. If the opposing decks have no Eldrazi, a resolved mid-game Altar of the Brood can mean good game. Phenax and Altar of Dementia work as well, combined with the mass of tokens.
Laboratory Maniac. There are a few instant-deck-in-graveyard combinations here, mostly revolving around Mirror-Mad Phantasm. Getting his ability off through Dimir Doppleganger, Body Double, Necrotic Ooze or Havengul Lich will ensure a Lab Maniac kill, if timed right.
Mortal Combat. Accompanied with the singing of the appropriate themesong.
Sometimes it simply wins through constant beatdown. Since the deck doesn't care about stuff ending up in the graveyard, I usually don't run out of fuel.
Svogthos, Nighthowler, Splinterfright and Revenant have all caused some pretty massive swings. I might want to get a Jarad, Lich Lord to fully capitalize on them. As well as a Lord of Extinction.

One thing this deck obviously hate is grave hate. But, as long as my creatures aren't instantly exiled but instead still hit the graveyard, I'm still getting value, which means I can keep on wailing on the player causing trouble using my zombies. The deck also has to lay low the first few turns if heavy aggro is present. The critical mass of tokens doesn't tend to appear too early, so in those first few turns, it needs to avoid the ire of said aggro player. Other then that, it's a rather resilient deck, having multiple avenues of victory helps a lot.

The main fun in playing with this deck is that every game plays out differently. You have to keep track of a lot, which makes it far from easy to use as well. But every game is a blast.

Huh, I'm not quite sure how I ever missed the Sovereign. That one's on the To-Buy-List for sure.
I have considered, and indeed tested, the drain-when-stuff-dies dudes, and I found their effect is either too easily dodged or just don't have enough impact, mostly because I'm not very highly stocked on sac outlets. Sure, they'd work nicely with the Stairwell, but I'm not too fond of using cards just to combo with one specific deck in the 99. The Stairwell itself, however, is on the "maybe - to test" list.
I should get another copy of Spitting Image. Currently, the one I have is in my Intet deck. I'm just not too sure I can reliably enough get both the land and the mana for the Image to keep working as it's quite a bit more situational than the Worm Harvest is. The Harvest will do its thing on an empty field with just Dakor Salvage/Life from the Loam. The Image also needs a good dude, so I'm a bit hestitant there, but I should give it a spin to try it out.
Thank you for the suggestions. Can't believe I never saw the Sovereign.

Testing a bit online has shown me Gravespawn Sovereign will indeed go in the moment I obtain one, let's hope the LGS has one in store. Fun card and not hampered by summoning sickness is awesome...