Based on the High Stakes cube here: https://www.mtgsalvation.com/articles/43059-high-stakes-magic-a-new-way-to-play
The basic rules are:

1. Players begin the game with 10 gold and no starting hand. Gold is a currency used to purchase cards that come up for auction. At the end of each player's turn, all players gain 3 gold.
2. Players do not bring decks to the table. Instead, a single stack of cards called the auction block (this cube) is shuffled and placed on the table.
3. The draw step is replaced with the auction step. At the beginning of the auction step, reveal the top card of the auction block. The active player may then bid an amount of gold for that card, including zero. In turn order, each player may top the high bid. Each player may only bid once. The bidding ends when all players have had the opportunity to bid. The high bidder loses gold equal to the high bid and purchases the card.
4. Upon purchasing a card, the purchasing player may choose either to cast the card immediately without paying its mana cost, regardless of timing rules, or to put the purchased card into their hand. Players may cast cards in hand without paying their mana costs. However, once a card is in hand, it must follow the normal rules as to when it can be played.
5. If the purchased card wasn't a creature card, repeat the auction step. This process repeats until a player purchases a creature card.
6. At any time, and as many times per turn as they desire, a player may spend one gold to add one mana of any color to their mana pool. This allows players to pay for certain costs, like kicker, cycling, or equip costs. It also makes cards like Mana Leak rather interesting.
7. Players play with their hands revealed. This is to prevent people from having to memorize cards they've already seen purchased at auction by the other players.