Imagine a standard pokemon game format of a preteen murderhobo, but the battles play as an exact copy of the card game with a slight difference, to build decks and stuff the same way you would for the card game, you find trainer cards by collecting cards in the world via loot rewards from battling other trainers and gym leaders, also finding secret items and buying them from pokemarts. But actual pokemon creature cards, you have to find them in the world by the normal means of wading through tall grass and dark caves.

This is where the differences are, in the normal card game, you have to ko 6 of the opponents creature cards, so in this game, a wild pokemon would be the only creature card with a few random trainer cards that fit with the level of the area you're in and you would only have to beat the one creature card to win, maybe reduce the creature card to 50% hp to capture it with a pokeball, and trainers would have from 1 to 6 creature cards for you to beat.

Other than that, literally everything else would play completely normally. Tile based adventure game with puzzles and all that. Maybe a remake or a modded rom of red / blue could work as the basis.