The pre-existing game engine with a bigger world and couple of new mechanics, in other words.
Not that TotK, or that approach to sequels, is even bad: I just wish Nintendo did less furiously masturbatory self-back-patting about how revolutionary it supposedly is. It is what it is (an acceptable if underwhelming sequel IMO), and Nintendo is what Nintendo is - a bag of dicks.
IIRC it is actually a different physics engine than BotW. BotW couldn’t handle all the physics interactions in TotK. That’s what’s so impressive about the game. Physics-based games are rare, especially for AAA-developers, because it’s just a lot of work. In TotK everything just works as you’d expect. You’re just looking at it from a gameplay perspective while ignoring the technical achievements.
