Hi Stumbler! Dynamitron here to assist you with any gameplay related FAQ ⚡
Stumble Pass is a monthly reward system in which players can earn skins, emotes, animations, etc. 
Rewards vary for each Season, and are divided into 2 types:  
Premium Pass:  
Has a cost of 1200 gems and you will be able to get in-game rewards that are more on the rare side 
Free Pass:
No initial cost to unlock it. You will be able to get more common in-game rewards
Thank you for being awesome!