This is a Grenzo, Dungeon Warden EDH deck which attempts to win in a few different ways but mainly by infinite mana combo into lethal, table-wide damage.
The first time I saw Grenzo, Dungeon Warden, I wasn't very impressed by him. A few years and a lot more experience later and now I see that I was wrong and, even with a budget, Grenzo can be a powerful commander. In this deck, I've tried to exploit Grenzo's abilities to their fullest.
Firstly, being R/B, mana is going to be difficult to come by for a while. We'll mostly be relying on our lands per turn but we do have a little ramp in the deck to move things along with cards like:
Coveted Jewel
Dreamstone Hedron
Vessel of Endless Rest
Leaden Myr
Iron Myr
Rakdos Locket
Rakdos Signet
Mind Stone
Hedron Archive
Ramp isn't this deck's strong suit and you'll want to make sure you can protect Coveted Jewel and Dreamstone Hedron as you will see later on.
After we get a mana base set up, we're going to need some cards and for that, I've tried to pick some decent and cheap draw spells to help us out. These aren't the most optimal picks but they do help keep the deck cost in check and they'll work for our purposes:
Ambition's Cost
Syphon Mind
Ancient Craving
Read the Bones
Sign in Blood
Faithless Looting
Disciple of Bolas
Smothering Abomination
Keep in mind that a few of our mana rocks will draw us cards as well. And aside from that, any time we get to scry, we also get to set up our next draw or Grenzo ability trigger so there's no shortage of card selection. With that in mind, let's go over what cards we're looking for and why. We have several ways to win or just generally gain advantage over our opponents:
Voltaic Construct + Toymaker + Dreamstone Hedron/Coveted Jewel = Infinite mana
+ Grenzo = Infinite commander damage and playing every creature in the deck
+ Exsanguinate/Conflagrate = Lethal table-wide damage
+ Banefire/Burn from Within = Single opponent one-shot
+ Pashalik Mons and a Goblin token = Infinite Goblin army (this combo in particular only works with Coveted Jewel)
+ Syr Konrad, the Grim = Either milling or pinging the table to death (also only works with Coveted Jewel)
+ Shadows of the Past = Lethal table-wide life loss (another Coveted Jewel-only combo)
Another good combination is Grenzo and Ashnod's Altar; if you don't like the creature Grenzo pulls, you can sac it to Ashnod's, get the 2 mana back and spin the wheel again.
There are a few more interactions here, like getting Flayer of the Hatebound in play and then using Grenzo and infinite mana to cast every creature in the deck, effectively burning all of your opponents to death at instant speed. Warstorm Surge can also kill opponents with Grenzo it will deal commander damage (while Warstorm is the source of the ability, Grenzo is the source of the damage). Also notice a few of the combos above are only viable with Coveted Jewel in play. Thankfully, we will have several ways to hit the cards we need:
+ Netherborn Phalanx (Transmute) will grab us any 6 CMC card in the deck which includes both Dreamstone Hedron and Coveted Jewel
+ Dimir House Guard (Transmute) is going to tutor our Voltaic Construct or another 4 CMC card if needed
+ Shred Memory (Transmute) will tutor our Toymaker or another 2 CMC utility
+ Behold the Beyond will grab our entire combo in one spell
+ Diabolic Tutor will get us any of the above, but particularly it can grab Behold the Beyond
+ Wishclaw Talisman is another card which will help us get into a combo, at the cost of helping our opponents but we should be able to take more advantage of this most of the time
So we have a good winning strategy but what happens if we lose a combo piece to Grenzo or our opponent's hate? I've made sure to include some ways of getting our cards back:
+ Reito Lantern will put a card from our graveyard on the bottom of our library for the low cost of 3 mana
+ Tel-Jilad Stylus will allow us to save a permanent at instant speed or return a creature to the bottom of our library for Grenzo to retrieve again
+ Vessel of Endless Rest, while mainly a mana rock, can help us retrieve something if we lose it
+ Whisper, Blood Liturgist acts as a creature recursion at the price of two creatures and we'll have plenty of goblins to feed her
+ Phyrexian Delver will retrieve one creature from the graveyard and bring it to the battlefield
+ Entomber Exarch is going to bring a creature from the graveyard to our hand
+ Junktroller will help us recur whatever we need to and put it on the bottom of our library
+ The Cauldron of Eternity returns our creatures to the bottom of our library automatically but it also allows us to bring them from the graveyard to the battlefield at the cost of 3 mana and 2 life
+ Elixir of Immortality is going to keep our graveyard moving back into our library as needed
Our set up for recursion will definitely help us stay in the game longer. But what about making sure our opponents don't go off and kill us? The thing we want to do most is stay alive and combo before anyone else. To do that, we need to minimize damage wherever possible:
+ Decree of Pain wipes the board and draws us cards
+ Plague Wind wipes every side of the table but ours
+ In Garruk's Wake will do the same as Plague Wind but it hits Planeswalkers too
+ Nevinyrral's Disk just in case we get overwhelmed by permanents we can't deal with otherwise
We can also deal with our opponent's creatures with our X-cost spells. Conflagrate and Burn from Within are great options to either clear the board or get rid of something Indestructible. If all else fails, I wanted to make sure we could go with a semi-Voltron route by spending as much mana as possible on Grenzo and then equipping him with Hot Soup and Swiftfoot Boots to take our opponents out with commander damage.
I didn't go over absolutely everything this deck is capable of but it is very versatile and can be very powerful with the right cards and in the right hands. I tried my best to make it both effective and affordable but if you have any questions, comments or noticed some mistakes I made, please feel free to leave some feedback below. Thanks for reading and happy brewing!