Labyrinth Warriors: The Rending Absolution
The fifth and final Labyrinth, and it's a tough one, even if you've been playing since the beginning. The enemies are much sturdier than the ones you fight in Abyss 12, so it's not easy to skip enemy phases by taking them out fast. No half-assed teams, make sure you're ready to dig in and survive.
It's a very different skillset from what Abyss has been encouraging, and I guess if endgame content starts trending toward this kind of thing I might be more inclined to pull for the likes of Zhongli or Kokomi in the future.
Only downside I can see with Labyrinth becoming an endgame mode is the randomness, you would want a team that can deal with just about anything. Especially since losing a fight means you start over from the beginning! Not just survival concerns, but having a large Hydro or Electro presence might be risky since they have so many bad elemental matchups.