Storm crow Highlander

Storm crow Highlander is a commander variant with following restrictions:

Aside from the normal 100 cards including commander you have one Storm crow in your deck
sideboard of 15 cards.
Your storm crow is of the same color as your commander.
You start game with storm crow in game.
You do not lose from going to 0 lifes, decking out, 21 commander damage or 15 poison counters until a storm crow gets a hit on you.
If your starting storm crow would be removed it phases out and all counters, enchantments and equipments are removed from it.

https://mtg.gamepedia.com/Storm_Crow_Highlander

Grand melee

Grand melee is a multiplayer format for more than 10 players

All the players sit around same table, but instead of the normal free for all game all your spells only affect to range of 1

No one else than the players right next to you exist for you until your neighbor is gone. If you play a card that wins the game only the players who are on your immediate right and left will have lost the game. If you play Obliterate it only affects the players right next to you.

You can have several turn markers running around but just keep them a bit apart from each other so you don’t have a player playing several turns in a row.

Real more:
https://mtg.gamepedia.com/Grand_Melee

Star

Star is multiplayer format designed for 5 players.

Each player takes a single color deck and a place on table according to the color star at back of the deck.
You win only by having your enemy color decks defeated.
You can attack anyone and target spells at anyone.

Little variations that you could have for bit change:

Have each player a tri-color deck with friendly colors [W(gu)] Bant, [U(rw)] Esper, [B(br)] Grixis, [R(rg)] Jund, [G(rw)] Naya
Have each player have a tri-color deck with enemy colors [W(bg)] Abzan, [U(rw)] Jeskai, [B(gu)] Sultai, [R(wb)] Mardu, [G(ur)]Temur
Have each player play with the allied dual color decks [W(u)] [U(b)] [B(r)] [R(g)] [G(w)]
Have each player play with the enemy dual color decks [W(b)] [U(r)] [B(g)] [R(w)] [G(u)]

or as we played it:

Each player can play any deck
if the 2 players in front of you die you win.

Which color would you rather have in the color wheel? Would you rather play a game in mono color wheel or one of the variations?

Brawl

Brawl is a 60 card Commander using only cards from standard so rules for creating your deck would be

1 Legendary creature or planeswalker that allows using it as a commander.
59 other cards with no more than 1 of each card except for basic lands, each of these cards must have same color identity as your commander.
All cards in your deck must be standard legal

When you have more than 2 players each player starts with life total of 30, if only 2 players then 25 is your starting life total.
First mulligan is to 7 cards
If your commander dies or is exiled you can set it to commander zone, each time you play it after first it costs 2 colorless mana more/times it has died.

https://magic.wizards.com/en/game-info/gameplay/formats/brawl

What would be your favorite Brawl commander from the current standard cards?

Two headed Giant

Two headed Giant is a way to play either Constructed or Limited games.

In Two headed Giant you play together with another player against 2 other players

You share life total and start at 30 lifes
You take turns together, you attack and block together.
First mulligan is to 7 cards
You do not share mana or cards.
Cards that target Each opponent counts it from both players so it works twice.

What would be the best team up of 2 decks?

Conspiracy

Conspiracy is a special set, and a card type. The set was created for drafting multiplayer drafts.

The special Conspiracy cards are not in your deck and are not counted for your deck limit, and you can have as many as you want of these conspiracy cards in the side of your deck.

Some of the conspiracy cards or “draft matters” cards within the set will ask you to write down a number or color or something else and they are normally drafted face up.