This is part 7 of the Memory Evaluation tunnel, which is also the last.
Note: Since you can only use the Gentleman in this tunnel, he will be the only recommended character.
The first half of part 7 is comprised of a single erratic line of tile, spanning across multiple sides, and two square platforms at the end.
It is recommended that you jump frequently during the second half of the level, especially if you can't see the dark tiles well.
Here is a brief description of the cutscene that featured in this level. More can be seen in this page.
Grand Opening Edit
The Gentleman introduces his new attraction, the Memory Evaluation. Unlike any tunnel ever before seen, it plunges you into darkness halfway through each level to test your memory. He opens the tunnel to the public, yet it was just for rehearsal. The Lizard is revealed to be with him, sleeping by the entrance.