If you wanted partner in grixis, I don't see silas renn, seeker adept being mentioned, who is passable if you wanted the artifact reduction route as a possibility. That said, for playing cheap spells with utility, why hasn't anyone mentioned evoke? Shriekmaw, mulldrifter, etc. are excellent cards on their own, do a fair amount of damage with vial smasher, and end up in the graveyard to fuel delve. All around excellent for your theme, I think. Other than that, I think with this style of deck, mizzix of the izmagnus would be an excellent addition in the 99. If you're playing a ton of high cmc spells with spell reduction costs of one kind or another, mizzix will get out of hand quickly.
Here is a mock up of a list for my deck using Vial Smasher the Fierce and Ishai, Ojutai Dragonspeaker. This is not my full list but it includes all the cards I am thinking of playing. I would like input on the cards I am playing, what other cards I should be playing, and if I shouldn't just be playing tri-color.
Credit to DolZero for this awesome sig!
1 Snapcaster Mage
1 Soulfire Grand Master
1 Monastery Mentor
1 Young Pyromancer
1 Baral, Chief of Compliance
1 Goblin Electromancer
1 Mizzix of the Izmagnus
1 Avatar of Woe
1 Avatar of Fury
1 Bedlam Reveler
1 Mulldrifter
1 Shriekmaw
1 Ingot Chewer
1 Metalwork Colossus
1 Necropolis Fiend
1 Fire Servant
1 Combustible Gearhulk
1 Kaervek the Merciless
1 Delirium
1 Deflecting Palm
1 Reflect Damage
1 Comet Storm
1 Prophetic Bolt
1 Curtains' Call
1 Divergent Transformations
1 Volcanic Vision
1 Force of Will
1 Snuff Out
1 Gush
1 Dig through Time
1 Thunderous Wrath
Sorcery
1 Temporal Trespass
1 Temporal Mastery
1 Bonfire of the Damned
1 Entreat the Angels
1 Rakdos's Return
1 Reforge the Soul
1 Blast of Genius
1 Wound Reflection
1 Repercussion
1 Baneful Omen
1 Everlasting Torment
Planeswalker
1 Sorin, Grim Nemesis