One of the best finishers in EDH, Insurrection, should be here.

I agree: I feel like I'm doing really well on the control elements, but I'm lacking powerful finishers. I'm building it mostly with the idea that Bolas himself will be my win-con, but that's not always feasible. I like Insurrection

Alrighty so the hardest part (arguably) about grixis is mana ramp/acceleration. Signets are all good and what not but personally I'd get rid of two of your signets for two of the following:Armillary Sphere, Gem of Becoming, or Everflowing Chalice

When you get the chance, drop Wayfarer's Bauble for Expedition Map

Lastly here are some cards that I think would benefit you through Nicol Bolas himself and should be considered. Dragonspeaker Shaman, Waste Not, and Sangromancer.- Takeouts for these Id suggest your duplicates Dack's Duplicate and Evil Twin, Notion Thief, or Propaganda. Propaganda is a good card, I personally just don't like how it meshes with the flow of the deck.Also someone once made a very compelling argument for me not to use Shadowblood Ridge and I agreed with them. Don't remember what that argument was but I've never really seen the point of using it, sure it can mana fix, but if you need all your other mana cant tap this for anything.

Also forgot to mention things like Thornbite Staff are good for bolas. Others to consider are Hermetic Study Viridian Longbow. And Warstorm Surge is pretty good if you are looking for Dragon Tempest redundancy.

Tiddilywinkus thanks for the suggestions! As far as Armillary Sphere and Gem of Becoming are concerned, I've actually tested those cards in earlier iterations of the deck, and in my experience they consistently under-perform. The problem with those cards is that they don't actually ramp me - they just fix my mana by putting lands into my hand - and I'm looking for ways to get more mana on board more quickly. For the same reason, I much prefer Wayfarer's Bauble to Expedition Map because the Bauble actually puts a land on board. Everflowing Chalice is definitely something to consider.

Dragonspeaker Shaman, while good with Bolas, isn't worth the inclusion here since there are so few other dragons in my deck. Most of the time he would just be sitting around as a 2/2 (and an obvious target to be removed as soon as possible).

Waste Not is interesting, and I would certainly accrue a lot of value if I can crack Bolas, but the only other cards in my deck that make opponents discard cards are Nicol Bolas, Planeswalker (with his ultimate) and Cruel Ultimatum - both of which are super high CMC and rarely see a lot of play. Due to the lack of other discard effects, I'm hesitant to include a card which does nothing if my opponents aren't discarding cards.

I do like the idea of Sangromancer - that can definitely buy me a lot of life over the course of the game, and can be a huge life-swing if I get Bolas online! I want to find a spot for her for sure.

Thornbite Staff and Viridian Longbow are decent choices to have around; they would give Bolas "pseudo-haste" for his discard effect. Plus they stick around if he were to be removed (which he so often is). I'm less keen on Hermetic Study, since Auras are almost always just straight card-disadvantage. Warstorm Surge is certainly something to consider as well - I do have a lot of high CMC creatures, and that damage could add up.

Thanks again for all of your suggestions!

Also, I know this list is missing Polluted Delta - I have one ordered and it's on the way. If you could help me find a land to cut, I would be grateful! (I'm not keen on cutting any more basics, but if you think there are no better options, then suggest a basic)

You could probably cut a pain land for Polluted Delta.

How good are Jace, Unraveler of Secrets and Ob Nixilis Reignited? Both seem sub-optimal. I like Ugin, the Spirit Dragon and the greatest thief in the multiverse Dack Fayden more. Or maybe replace one of them with that Pull from Tomorrow in your Maybeboard.

I'd look into upgrading your Archaeomancer to a Snapcaster Mage, if you feel like spending that kind of money.

With 10 counterspells, Baral, Chief of Compliance would be a good add.

Wayfarer's Bauble might be better as Thought Vessel or Expedition Map to get Reliquary Tower consistently as you want to keep you hand full.

I'm not a huge fan of Dragonlord Silumgar as an opponent can get the thing you stole back, if the stealing was permanent I'd like it more. Duplicant and Noxious Gearhulk would be good replacements.