Brainstealer Dragon is really good, I would add it back in, I've been running it in chainer and it has been surprisingly good. Elder Brain is also fun, I've been running it in Isshin and it has been hilarious. Looking at your maybeboard there is an argument for many of those to be added.

Up the amount of control, run maybe 5-7 counterspells. Probably need more draw as well, you could use the usual Ponder, Brainstorm, Preordain, and the like, as well as some stuff like Blue Sun's Zenith, Gadwick, the Wizened (it may same janky but can help your creatures push through after the draw effect), and Lim-Dul's Vault.

Sweet deck! Only suggestion I have is Aqueous Form over Slip Through Space

I like the direction you're heading. Still has some fat to trim down to get it more streamlined though. Have a look at Filthy wHorrors and see if it gives you any ideas, it's my rework of the same pre con deck