Rhythm Dogtor

Rhythm Dogtor is a secret level that can be accessed by pressing right and left in a certain order. It is a dog parody of One Shift More. It is made by Morphious86.

How to get to the level
To get to the level, you have to do a certain code, which is right, left, right, right, left, right, left, left, right, left, right, right, left, right, left, left.

Trivia
According to Healion123, you have to beat Act 3's boss stage and do the code quickly enough.