Post-game. After saving 808 and jumping over the gap between buildings. If you climb towards the route out, and then turn around, you’ll see a Peppermint shield to destroy.

Destroy that barrier and then grapple up.

Just before the final boss in Track 2, in the reception area, you’ll see him staring at a poster on the wall

In Lab 44, after you learn how to parry.

After punching the rock and you’re on the platform, go to the right and jump over the lava, and then jump onto solid land beyond that. Follow the path upwards.

in a 2D section after Node 1, before dropping down off the edge after the lasers, turn around and jump up into a hidden passage of sorts above you.

After the 2D section in Track 7, you’ll use a jump pad to go up. When you're in that corridor, go forward and climb up to the right. Then jump to the wall on the opposite side, and then jump up to the top above the jump pad.

After the fight on the falling platform in the museum (the one that will drop and destroy an exhibit), look to the left.

After using the rail transit system in the atrium , you’ll come to a magnet grapple barrier that Peppermint has to destroy. There’s a platform off the left-hand wall.