Limited edition cards, those from early sets (1999-2003), and cards with special promotional or tournament origins are often the most valuable
Also, since players are using Tool Scrapper less and less, your ACE SPEC might just stick around unopposed
Macar, Gilded Sorrow : personally I think treasure works better than gold just because it's a better-known token, but up to you
Completing a dungeon will also allow specific ability text on other cards to be used, with Gloom Stalker and the very meta Dungeon Crawler revealed as two such cards that gain benefits from a completed dungeon - double strike and the option to return to the player's hand from the graveyard respectively
While Journey Together brought back Trainer Pokmon, Destined Rivals nailed it by bringing back fan favorites Giovanni and Team Rocket alongside Ethan, the protagonist from Pokmon Gold and Silver