"Arena" Analysis final 3 still locked?

[Ungodly Fetus]

NG+++ done every option i can think of the first 3 playthroughs, only saw 2 endings? did i miss one? do i need to find certain downed AC's or equipment? checked every mission to see if any unlocked, still nothing, what am i missing?

[Jagdtiger]

They will not complete until you go through the third ending, which should be unmissable if you only select the new missions when they become available

[D. Flame]

First play-through: Liberation or Fire Ending

2nd play-through: Whichever of the two Endings you did NOT see the first time, unlocks special arenas

3rd play-through: All Mind Ending (requires completing both of the other two first), unlocks last 3 hidden arenas

[This PC]

You also need to follow a fairly precise path to get the true ending.

[C1REX]

The last 3 AI arena bosses are only availbable if you follow the route to true ending and they become available almost at the end. So they are very missable.

The true ending and the real final boss is worth to replay the game. This will also give you achievments for all missions and access to secret coral parts and weapons.