I've been messing around with a more dedicated Storm build that cuts the Doomsday stuff.

One thing I discovered when playing it that I think you can translate into this list without any difficulty is Remand.

There are plenty of situations where it's useful interaction early to prevent an opponent from going off, and it doesn't really hurt you much to cascade into as a counterspell. Sometimes it even generates a massive amount of value (Remand your own Mind's Desire OMEGALUL!).

Try it. I think you'll like it.

I tested Remand a lot in the beginning of the deck, and thought that it wasn't necessary. The ability to bounce your own storm spells is almost never anything more than overkill, and the fact that it doesn't actually counter an opponent's spell is more often a negative factor. Cascaidng into it is still usually pretty bad, but if there are a ton of control decks around you, it may be worth an inclusion. I think Unsub is actually a better slot as it can act as removal for other commander-centric decks like Zur or Tamna.

Unsub is the other card I was running in that slot! I've had some trouble deciding between the two and ultimately went with Remand because I've had a fair number of times where I'm going off and start to run out of gas and have some piece of more narrow removal left that doesn't do anything else as my last card (Fire Covenant that holds the spot of Toxic Deluge in your list, oh how you occasionally vex me so) and I cast it hoping for a last chance cascade luck sack top deck only to hit... Unsubstantiate. When this happened with Remand I at least got a new card out of the deal and sometimes hit more gas, so I made the switch. I feel like there are enough controlling decks in my usual group to warrant it, but I feel much more encouraged about both options after hearing it from you and I'll probably swap them both around at random until one cements a place in my heart.

I've always been curious but why is Grim Monolith being run in a lot of Cedh storm lists? I can't really see a reason for it but I'd be glad to gain some insight as to why it's being used

A.) It's a mana accelerante, casting it turn one can lead to some explosive starts, or you could just play it on turn 2 to set up a turn 3 with six or more mana.

B.) It's a ritual that costs colorless mana. You cast it off a mana crypt or a mana vault or a sol ring or a mana drain with no real determent to the colors available to you.

C.) Most importantly it's reusable. It adds one storm and one mana on your winning turn, and you can bounce it back to your hand, so it has immense value with Outcome, Chain, and Hurkyl's.

Ah, okay. Thanks for explaining that, I always under the impression of Storm being dragged down by effects like Grim Monolith because of needing a somewhat higher coloured mana density in comparison to say Chain Veil Teferi. Admittedly, although I have the capabiities to play this list in paper, I do very much struggle understand the principles of manually storming off via Yidris' cascade or even without it.