Rules here: https://sentineloldschoolmtg.com/old-school-brawl-a-93-94-commander-variant/

Basically, commander with the following restrictions:

• 1 commander (summon Legends + some mono-coloured, see link)
• 59 other cards in the deck from the colour(s) of the commander
• singleton = no more than one copy of each card (except for basic lands)
• sets from old school
• banned list: City in a Bottle, Karakas and Mind Twist
  • optional: Ancestral Recall, Mind Twist and Braingeyser (blue is already strong enough)
• no sideboard

Links:

• Brawl!, 31/12/2021

My first attempt was with Xira Arien (01/04/2022).