To get to the secret ending, you must play the Level 79 - Shift.

There are 4 sections that you can move.

First - Lower down the 3rd section

Second - Move the 2nd section upwards

Third - Go to the top of the 3rd section

Fourth - Move the 3rd section upwards

Fifth - Jump and Go right

You'll find a passage, and you'll found him standing in front of the wall or something.

To make things faster, Lift down the 2nd section, Go to the top of 2nd section, Lift up the 2nd section (make sure that you don't crushed), Jump and go right.