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If you are buying the Season 28 pass (which is a sweet deal because it has more rewards than usual, in both free and paid tracks), you can unlock Jackpot for much cheaper than it would typically cost from special summons gates.
However, Jackbot is best at 1 star with the Equipment Drop Chance skill, and it isn’t easy to get his shards even once unlocked (he can rarely proc himself and he can appear in summon gates) so you can get a head start if you purchase the Super Battle Pass this season, and then first use the 5 recruitment posters at the end of the SBP towards Jackbot (you can only use them towards heroes you haven’t yet unlocked), then get the 10 shards from the BP (which will unlock and give you 5 shards towards 1-Star), and then use the 5 gym-passes to get him to 10 shards. You will still need 10 more shards but hopefully you will be lucky with the summon gates - or you can try to get 10 more gym passes (either from future SBP’s or outright purchase when on offer)
Note: This recommendation is for casual players (who are not trying to unlock the premium heroes) who are looking to spend a bit of money to up their game. If you’re working on premium heroes (from special summons and/or tower points) you probably already have Jackbot anyway.