Minigame: Critical Roll Casino Dice Game

This is a casino-style dice game inspired by Blackjack. It could be a fun game in its own right totally independent of an in-universe tabletop RPG mini-game, but by using dice and playing into the idea of a critical roll, it has a fun tabletop feel to it.

The Rules

• The goal is to roll the closest value to 20. 
• Unlike blackjack, there is no busting, but on a tie in different direction (e.g. 18 vs 22), the lower value takes priority.
• Players can play against each other or against the dealer.
• Place bets and after all bets are placed, everyone rolls a d20.
• Critical Success: On a roll of 20, the player automatically wins and receives 1.5x their bet.
• If the dealer also rolls a critical success, it's considered a push and the player neither wins nor loses.

• Critical Failure: On a roll of 1, the player automatically loses.
• After the d20 roll, place the d20 facing the rolled value below the bet. Each player takes their turn from left to right (house goes last). Each player takes all of their actions before moving on to the next player.
• Hit: If the player did not roll a critical success, they can choose to roll a d12 and add the value to their total, placing the d12 facing the rolled value under their d20 in a dice chain. Players can continue to hit, decreasing the dice size until >= 20, or the player has rolled a d4. 
• d12 -> d10 -> d8 -> d6 -> d4
• Critical Hits: Rolling the maximum value on a die is a critical success. Roll a d20. If the player rolls a 20, replace the current total with the 20. This is not the same as a critical success. A roll of 1 on this die does not count as a critical fail.
• Miss: After rolling a 1 on a die, add the 1 to the total, but the player cannot make another hit even if they have smaller dice (e.g. if the player rolls a 1 on a d8, they cannot hit to roll a d6). This is not the same as a critical failure.
• Split: If the value of a rolled die is the same as the directly preceding die in the chain (e.g. 5 on a d20 followed by 5 on a d12), the dice chain can be split.
• Separate the dice and place a bet equal to the original next to the second die.
• Start from the first die and decide whether or not to roll another hit (e.g. go back to the 5 on a d20 and decide whether to hit with another d12). Follow this chain, then move to the next (e.g. after finishing the d20 chain, go to the 5 on the d12 and choose whether to hit with a d10).
• A dice chain can be split as many times as there are valid opportunities and the player can afford the bet.
• Double Down: Rather than taking a hit after the d20 roll, the player can choose to double their bet, and roll one single die of any size besides d20, but they cannot take any other actions after the double down.
• Dealer Rules: 
• If the dealer and player roll the same value, dealer always wins (except critical successes, which push).
• A roll of 1 on a d20 does not count as a critical failure.
• Cannot split or double down.
• Must hit until they have a value >= 20. 
• No critical hits or misses.