My original build of this deck was a much less combo focused so I have a couple recommendations. Some of these are pretty meta dependent/ maybe not that great.
Netherborn Phalanx - If people are flooding the board with creatures/tokens in your meta this can just one shot people. Obviously not a great early flip.
Anathemancer - Similar to Phalanx but for non-basic lands.
Guiltfeeder - Can hit for a lot late game and comes with some evasion.
Great primer, Grenzo was the first EDH deck I ever made. I had kind of taken it apart over the years but after I saw this primer I've started rebuilding him.
Looks like we got a couple of goodies from Dominaria, Zhalfirin Void gives us an untapped scryland and Whisper, Blood Liturgist is Hell's Caretaker without the timing restriction, though we do have to sac another creature, might be good if we want another thornbite staff combo.
I've found a couple cards I think might be worth consideration while I've been rebuilding my Grenzo deck so I thought I'd post them here.
Buried Ruin - With how crucial our artifacts are for our combos this seems like a nice way to pick up a flipped/destroyed artifact. We're two colors so I figure the colorless mana doesn't hurt too much.
Agent of Erebos - Seems like the best graveyard hate we can add to the deck, a flippable creature and is four mana for our tutors.
Ravenous Chupacabra - I have this in my list over Bone Shredder, one more mana to hardcast but it can kill anything. Also makes it tutorable.
Crypt Rats - Mana hungry but I feel like having a access to a board wipe could be strong. Also deals damage to players.
Yahenni, Undying Partisan - If we need another sac outlet this seems like a good option. Instant speed sac and can survive a board wipe, get huge, and beat down. Also make a good blocker.
Arcbound Reclaimer - Not sure the deck needs more artifact recursion but this seems like a decent choice if it does.
Dualcaster Mage - Not a very good blind flip but in a very spell heavy meta it could do some work. Seems fun once you have a digger loop active.
My original build of Grenzo had way too many non-creatures but there were a couple I would consider running.
Mana Geyser - This card very easily makes 20+ mana when cast and can let us dig super deep into the deck. Out of all the non-creatures I ran in my old build this one seems like the most likely to make it into my new build.
Braid of Fire - Games when you cast this on turn two feel so great. But being a dead flip and a pretty dead draw late game makes me lean toward not putting it in my new build.
Netherborn Phalanx - If people are flooding the board with creatures/tokens in your meta this can just one shot people. Obviously not a great early flip.
Anathemancer - Similar to Phalanx but for non-basic lands.
Guiltfeeder - Can hit for a lot late game and comes with some evasion.
If you want to flip some large creatures Ignition Team and Nighthowler tend to be quite large.
If you're on the go wide plan yourself, Purphoros, God of the Forge and Ogre Battledriver seem good.
Similarly, Archetype of Finality makes your go wide strategy hard to attack into/block and combos well with Goblin Sharpshooter and similar cards.
Another random suggestion Soulbright Flamekin can turn 6 mna into 8 mana and give your creatures trample in the process.
Hopefully one of those random suggestions was helpful.
Looks like we got a couple of goodies from Dominaria, Zhalfirin Void gives us an untapped scryland and Whisper, Blood Liturgist is Hell's Caretaker without the timing restriction, though we do have to sac another creature, might be good if we want another thornbite staff combo.
I've found a couple cards I think might be worth consideration while I've been rebuilding my Grenzo deck so I thought I'd post them here.
Buried Ruin - With how crucial our artifacts are for our combos this seems like a nice way to pick up a flipped/destroyed artifact. We're two colors so I figure the colorless mana doesn't hurt too much.
Agent of Erebos - Seems like the best graveyard hate we can add to the deck, a flippable creature and is four mana for our tutors.
Ravenous Chupacabra - I have this in my list over Bone Shredder, one more mana to hardcast but it can kill anything. Also makes it tutorable.
Crypt Rats - Mana hungry but I feel like having a access to a board wipe could be strong. Also deals damage to players.
Yahenni, Undying Partisan - If we need another sac outlet this seems like a good option. Instant speed sac and can survive a board wipe, get huge, and beat down. Also make a good blocker.
Arcbound Reclaimer - Not sure the deck needs more artifact recursion but this seems like a decent choice if it does.
Dualcaster Mage - Not a very good blind flip but in a very spell heavy meta it could do some work. Seems fun once you have a digger loop active.
My original build of Grenzo had way too many non-creatures but there were a couple I would consider running.
Mana Geyser - This card very easily makes 20+ mana when cast and can let us dig super deep into the deck. Out of all the non-creatures I ran in my old build this one seems like the most likely to make it into my new build.
Braid of Fire - Games when you cast this on turn two feel so great. But being a dead flip and a pretty dead draw late game makes me lean toward not putting it in my new build.