Cloned from Irrelevent's DESCEND INTO AVERNUS [Grixis] with modifications
Draft 3 packs of 10 cards (or 11 if starting out) to build a commander deck
3-4 player multiplayer
100 starting life
20 card deck
Each player starts with a Descent into Avernus in play that cannot leave the battlefield
Don't bother with lands
(There's also a fairly intuitive tiebreak rule. If all players go below 0 life at the same time, the player with the life total closest to 0 wins.)
Each color is uniquely strong at a few things. Additionally, each color pair has suggested (though by no means limiting) archetypes in addition to the commander-specific and Grixis options.
Blue is able to do a little bit of everything. It has the highest proportion of instant-speed effects and the most efficient counterspells.
Black specializes in creature removal. It also can play a longer game with lifegain effects and graveyard recursion.
Red brings the highest proportion of copies and forks. It also has the best ways to generate a mana advantage.
Control the board and the stack with flash creatures and blink effects. Games end quickly, so have a way to turn the corner.
Storm off with X-spells, or copy opponents' spells for your own needs.
Put permanents into play that limit opponents' options and hasten the end of the game.
Mill & Anti-MillWith 20-card decks, mill is a potent strategy. Be sure to have a plan!