The List

Legendary Creature — Octopus Rogue

Whenever Marvo attacks, clash with defending player. (Each clashing player reveals the top card of their library, then puts that card on their choice of the top or bottom. A player wins if their card had a greater mana value.)
Whenever you win a clash, draw a card. Then you may cast a spell from your hand with mana value 8 or less without paying its mana cost.

Marvo, Deep Operative

What are the Odds?

This is the actual decklist that I own.
Draft the Commanders first from a special pool (in the sideboard) with 4 packs of 10 or 12.
Each commander has partner. If you want to use one of the companions, you can do that as well if you abide by the companion rules and color identity rules. For Umori specifically, you may still have creatures as your commanders as long as the rest of the deck follows its companion rules.
I suggest choosing your commanders (and sometimes a companion) before you've drafted from the main pool. 
Each player automatically gets a command tower and an arcane signet.
Before drafting, players can decide if they want to draft 60 card commander decks or full-sized 100 card decks.
Draft 4 packs of 14 for 60 card decks and 6 or 7 packs of 14 for 100 card decks.
Color Identity does not matter when it comes to lands.
Draft Archetypes:
Reanimator
Cast spell, get value
Freecasting
Theft
Copying spells
Value for targeting your own creatures

(The Real) Budget Spellslinger Commander Cube

Draft the Commanders 1st from a special pool with 4 packs of 10 or 12 (This is that pool).
Choose your commander before or after you've drafted from the main pool. 
Main pool: https://manytcg.com/decks/cmggmq7en0001jo04ahw49ec6)
Each commander has partner. If you want to use one of the companions, you can do that as well if you abide by the companion and color identity rules.
Each player automatically gets a command tower and an arcane signet.
Before drafting, players can decide if they want to draft 60 card commander decks or full-sized 100 card decks.
Color Identity does not matter when it comes to lands.



Commanders for drafting the spellslinger budget commander cube

I realized that the main problem with the last iteration of this Cube was it included white. That pillar was taking a lot of space that could have gone to red and other colors. It seemed to dillute the experience so I made another one without such a useless color.
Special Rules:
Draft the Commanders 1st from a special pool (in the sideboard with 4 packs of 10 or 12)
Each commander has partner. If you want to use one of the companions, you can do that as well if you abide by the companion and color identity rules.
Each player automatically gets a command tower and an arcane signet.
Before drafting, players can decide if they want to draft 60 card commander decks or full-sized 100 card decks.

2nd Spellslinger Commander Budget Cube (Refocused)

The rules are, each player automatically gets an arcane signet and a command tower before drafting even begins.  Also, you can break commander color identity rules if you have to.

Commander Cube

Source: https://magic.wizards.com/en/news/announcements/murders-at-karlov-manor-commander-decklists

Marvo, Deep Operative

Rules Text

Card Facts

Legality

Rulings

Every version

Decks using this card