He mostly exists to enable Islandwalk for Merfolk, given there are cheaper ways to untap your stuff
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Promo cards are released outside of standard booster packs, through things like: Elite Trainer Boxes (ETBs) Special collection boxes Event distributions Movie tie-ins Pokemon Center exclusives Promo cards have their own numbering system (usually with a prefix like "SWSH" for Sword & Shield promos or "SVP" for Scarlet & Violet promos)
So, anything with a good activated ability that requires you to tap your creature (Palladium Myr, for example) can be used twice each turn or used, and you can still attack with it
I think there might be an easier combo, but I am curious how easy this one currently is for you
Being able to sort through cards by which booster pack they belong to is an important asset to Pokmon TCG Pocket