Force of Will, Force of Negation—oh yeah.

Wild Pair seems like it might also be good, if perhaps a little slow. Dual Nature is kinda similar, but hits everyone. There's also Lurking Predators, which is kinda similar.

Lands: Flooded Grove, Sunken Ruins, and Twilight Mire are good in 3 color, and you appear to have an abundance of basics you could hew from. I also like Reflecting Pool and Exotic Orchard in 3 color+. Also good are Prismatic Vista and Fabled Passage, even if you don't wanna bother with the etb tapped Evolving Wilds and Terramorphic Expanse. Path of Ancestry and Opulent Palace are also worth considering, if you can get over their tappedness. Could also consider the omnipresent Vesuva and Thespian's Stage for other people's good lands or for your Cabal. I also rather like Alchemist's Refuge in these colors, and Ancient Tomb in general, which is also kinda thematic with your Gorgon general. Also Temple of the False God. And Nykthos, Shrine to Nyx might be super good with all your blue dudes. That means you could also run Deserted Temple (and run with a mini temple theme) for your Cabal and Nythos, as well as potentially your copylands. Finally, Strip Mine never hurts, unless you want to maintain more basics.

I'm not seeing Sol Ring! Fellwar Stone is also good, though I'm not sure you need another. Also, Mana Crypt, but yeah.

You've got Demonic Tutor, might as well run the superior Vampiric Tutor as well.

Genesis Wave might also be good, again, if a bit mana-heavy. In the same vein: Omniscience. Card's an obvious bomb with your general, I wouldn't shy away from it. You could also combo out with Null Profusion and/or Recycle, but that might be a line too far. Or maybe not, it's not exactly "infinite" per se! I encourage you to run em, go big on the Janktown Express.

Thassa's Oracle might be something of a win-con for you, and it's not bad with all your blue dudes either way.

Villainous Wealth from the new set is kinda cool, but maybe not entirely necessary.

Kydele, Chosen of Kruphix is a neat mana source, especially when you compare her to something like Thran Dynamo. Might be worth considering.

Alhammarret's Archive—again, maybe a little slow, but 14 cards every turn? Thought Reflection, too. Could be game-enders, especially if you're running Omniscience.

Abundance is also kinda neat for your draws–can guarantee no lands if you don't want em. Might be a little underwhelming, but might be a bomb, I'm not sure.

Burgeoning is almost must-run with this general, also, now that I think about it. You'd be way ahead of everyone all the time with it and your general.

Alright, that's all I can come up with at the moment, but I reckon that's a good amount of adds to consider for you already 104 card deck. A few of these I feel like you really should work in there. I'll take a look at potential cuts a little later!

[https://tappedout.net/mtg-decks/persistant-plasm/?cb=1587692703]

Here’s the raw list I mentioned! You might find a few gems. Speaking of tutors, Secret Salvage was one I didn’t see on your list and seems real good. Started this collection of ideas so I could slowly start picking up cards for it and build someday. Thrumming Stone was a spendy one. Will play with Mill self/Others but might gen swing with Mr. Mims. I probably wanna hit a lot of graveyard opponents stuff if I can find room like the good ol’ sexy Wrexy days... Dimir mill life was good but Sultai will be hot! RIP Phenax

Did a search for (non-Planeswalker) permanents that say "untap all". Only 33 hits across all magic. Here are the ones that might be useful for you, beyond Seedborn:

Quest for Renewal (thanks Isabelle)

Awakening Probably worth hooking others up if played as a finisher

Curse of Bounty Could be very interesting

Faces of the Past

Murkfiend Liege This one seems super good

Knew I forgot something we talked about:

Lion's Eye Diamond

Grim Monolith

Mox Diamond

Chrome Mox

Hog town