Checkpoint Challenge Tokens are used specifically to enter the Checkpoint Challenge event.
 
It costs 1 Checkpoint Challenge Token to enter the Checkpoint Challenge, or to re-try the challenge if you are knocked out of the event.
   

Checkpoint Challenge Tokens can be earned through daily ad watches and acquired through Gem and in-app purchases. Checkpoint Tokens can only be acquired with Gems, purchases and ads when your token balance is 0.

Please note that only 20 Checkpoint Challenge Tokens can be stored at one time. Any additional Checkpoint Challenge Tokens earned will be converted into Gems automatically.