Use 20 of them to get Jackbot to 1 Star and unlock the first Equipment Drop Chance skill, because that makes him an even better farmer and also there’s no easy way to get Jackbot shards even if you’ve unlocked him: You can get them from Summon Gates but with a 1/16 chance that’s an expensive way to star him up. Jackbot’s skill can proc himself but this is very rare.
If you have more Gym Passes,
- Save them until you unlock Premium Heroes and use them to star them up
- You could use them to star up Jackbot to 4* and unlock the 2nd Equipment Drop Chance - but this is not as efficient a use of Gym Passes
- I do not recommend using them for the Open Heroes
In any case, don’t use the Gym Passes until you have enough to star up the hero - better to keep your options open