CARD ADVENTURE

An open-world card game RPG where the enemies you fight, places you explore, and quests you complete become the cards in your deck. Whenever you beat an encounter, you get a card related to the enemies; fight a gang of goblins and get a "Goblin Strike" card, fight a ghost and get an "Ethereal Dodge", etc. Probably get up to 3 duplicates or something idk. The cards in your starting deck are weak, so you want to start using new ones right away.
	Bosses and mini-bosses give unique and stronger cards. Same for finding hidden treasure chests in special locations, or completing side quests. Or they might give an equippable item that gives a passive bonus, either in addition to or instead of a card. Unique cards get to be more powerful because the event is more significant; if you find a secret dungeon with a treasure at the end, it would suck to get a card that's not worth using over the cards you got from basic enemies. Your deck is a photo album of your adventure, do you really want to remember the 3rd fight against slimes instead of the secret dungeon you found?
	But maybe you really like slimes, and enjoy their "Squishy Guard" card, so let's have a simple upgrade system. Maybe your cards upgrade if you get extra copies of them, or maybe it uses a special resource, maybe you need to fight Giant Slimes to get Squishy Guard+. In any case, players should only really get upgraded cards if you're actively seeking them out, otherwise the whole "unique cards aren't worth using" problem happens again.
	I imagine the power levels being like this. Level 1: Starting deck cards, kinda weak, enemy cards are often straight upgrades. Level 2: Enemy cards, slightly stronger than starting cards, decent. Level 3: Mini-boss/secret area/side quest cards, and upgraded enemy cards, slightly stronger than level 2, you could definitely beat the game with just these if you wanted. Level 4: Boss/special secret area/major side quest cards, strong but rare with complex effects. Each level is only slightly stronger than the last; strong enough that you can use it if you want to, but not so strong that you HAVE to use it.
	As you get further, you'll get more and more cards, so the deck size should expand over time to give you more room to put in cool cards you earn. But a bigger deck is suboptimal, so it'd be mean to force that on players, so make it optional with rewards; as you progress, you unlock passive buffs/item slots, but they're only usable if you have enough cards in your deck. Maybe also scale HP with deck size, to let fights be short in the early game and longer in the late game.
	The plot would probably be kinda Breath of the Wild style; there's some Evil Thing in an Evil Castle that you need to go fight, but you need to get stronger first. Maybe the gate is blocked and you need to beat 3-5 bosses to unlock it, or maybe you can just waltz right in with your starter deck, idk. You definitely don't need to go everywhere and fight every boss; it's YOUR adventure, you get to decide where to go and what to do. You probably don't even need to fight half the bosses to be ready for the final boss.
	I imagine the combat being Slay the Spire style, but it's not really important