Maybe I don't play enough deckbuilders, but it seems like there was a decent amount of new concepts in here that didn't directly come from other games. Abilities like Innate, Retain, Ethereal, cards getting upgraded for all future encounters every time they're played, costs of the card being reduced based on something specific happening that encounter, the stances of the Watcher character in general, and all the cards surrounding that idea, The orb idea for the Defect in general and all cards revolving around that idea, cards giving you bonuses if it kills a character, sometimes permanently, etc.
Even something as basic as all the cards costing energy to spend and you have only a certain amount of energy every turn (that can be increased by other methods), forcing you to prioritize what to play, as opposed to just playing everything you draw and only the order matters, like in most deckbuilders, changes the feel quite a bit.
They were able to take advantage of the video game concept (allowing cards to morph within an encounter and over the course of multiple encounters) and put it to good effect. Technically you could do that with a board game with stickers or something, but it's a lot more effective here, and only permanent for a run as opposed to forever.
That being said, they did take a ton of ideas from existing games. It just feels a lot more inventive than most deckbuilding games I've played, where most of them feel like some combination of Ascension and Dominion, with little to differentiate it.