There are two pickups in 'Invert', pickups are small black squares.
1. Level 5.1 @0:06
When you reach the end of the level after the spikes stay on the bottom (top) and follow the path to the end and the pickup is there.
2. Level 5.4 @0:18
As soon as the level starts swap to Thomas
/
move left a bit and jump
as the pickup is above Thomas (I already picked it up in the video, its where im jumping)
Here's a video