These are called minigame coins! You can use them to buy lobby and in game cosmetics, like kill effects, bed break animations, victory dances, etc. A wide variety of cosmetics to buy from, so it's good!
You can also donate them to your guild; 2 minigame coins = 1 guild coin. Guild coins are used to buy guild exclusive "skills" (and also cosmetics". These skills can help you get more experience to level up, a higher chance of getting mystery boxes, etc.