With Super Mario Odyssey, Nintendo came close to maxing out on the concept of being anyone you want to be. While that made for a one-of-a-kind experience within the Mario universe, there were actually a few other games that used the same hook first. One example is Everything, a game from animator David O'Reilly (Her, Mountain, Adventure Time, Eat My Sharts).
The main difference is that Everything doesn't set you out on a quest to rescue anyone, or to go anywhere in particular. Odyssey breaks down the barriers between player and non-player characters, but it never forgets that it's ultimately a Super Mario game, meaning that in the end, it's still about running, jumping, and saving Peach from Bowser. Everything isn't constrained by those conventions. If you decide to be a rock, then you can just roll around and live like a rock if you want. Why would a rock care about saving a princess? Why would some discarded bird feathers want to do anything other than float around on the wind?
If it sounds like Everything is a game about nothing, then that means I'm halfway to describing it properly.