Only Star Passes purchased with Robux are tradable. Star passes summoned from the banner before 7/1/22, however, are still tradable.
Overview
The Star Pass from Banner Z.
The Star Pass is a progression system that was added as a part of Update 27. There are multiple tiers which give certain rewards for each tier such as Units, XP, Coins, Gems, and Capsules. There are two tracks: a free one and Star Pass Ultra, which offers additional rewards on top of the free track. The Star Pass Ultra track can be unlocked by using a Star Pass Ultra unit, which can be obtained via Banner Z in World 2 as a 6-Star, evolving 1 Mysterious Key and 20 Current Capsules, trading, or by purchasing it for 799 Robux.
You MUST unlock your Star Pass from your inventory in order to use it. It won't work if the Star Pass is locked.
If you accidentally fed your Starpass units recently, you can use /restore, under the settings icon (gear) to restore them.
Deal some amount of damage (not necessary, but the result from staying alive up to Wave 15)
XP gained from matches don't carry over to the next tier, so any excess XP earned will be discarded. As higher the tier get, the more XP you will need to fill out the XP bar.
Through testing, most if not all game modes give the same amount of XP regardless of Normal or Extreme pass a certain point, some noticeable examples before this happen:
Earlier Story Mode such as Beginner Saga, Hidden Village and Desert Island up until Snowy Town on Normal difficulty. Which give increasing amount of XP up to the point of giving out the same amount as their Extreme difficulty counterpart. They start to give the same amount for every maps on Extreme difficulty starting from Desert Island onward.
For some unknown reason, Tiers 24 and 69 of the Season 1 Star Pass did not contain rewards.
The Skip Tickets were part of the tier rewards with it's unknown purposes until they got removed at the huge update. It was replaced by the Tickets for Ticket Quest in Season 3 onwards.
EXP Boosts were part of the tier rewards until they got removed along with it's feature at the huge update. It was replaced by Stardusts in Season 3 onwards.