You find the gambler in the left back of the tavern.
You can bet gold and mushrooms. The gambler hides a ball under one of the cups and shuffles them.
Now you have to guess under which cup the ball is. If you guess correctly, you'll win your stake twice. If you guess wrong, you'll lose your bet. While the gamler is displayed, you can enter /gold bet <amount> or /mushroom bet <amount> in guild chat to place bets. If you bet but leave the tavern, the game will automatically select one of the three cups for you.
The chance to win is 1/3.
Game of dice
You get five dice and have two tries per round. The goal is to roll three or more of the same symbols. In order to save dice for the second roll, you have to click/tap them. The more identical symbols are displayed after the second roll, the higher the prize.
The prize must be actively collected. If you fail to collect it and roll the dice again, the prize is lost.
You can play up to ten dice games per day. After every completed dice game you have to wait 60 minutes. The waiting time can be skipped with an hourglass.