[Mac Sirloin]

That's not the Ogmo level. The Ogmo level is in Chapter 2. What you are talking about is called a Glitch Level. There is one for every chapter, but unlocking them is completely random. Occasionally, when you start a level, you will hear a strange noise, and see Bandage Girl spinning around and glitching. If you make it to her when she is doing this you will unlock the Glitch Level.

An easy way to force it is to start a level where you can see Bandage Girl from the beginning, and keep killing yourself until she starts glitching. Try to do it on an easy level, one that you are fairly confident you can make it through in one try because if you die you are going to have to do the whole thing all over again.

Edit: I forgot to mention that the glitch levels are some of the hardest levels in the game. They aren't as bad as The Kid, or the Dark World of The Cotton Alley, but they are pretty damn tough. If you are having a hard time with it, I wouldn't worry about it. Come back to it once you've gotten some later Dark World level experience.

I bet they're going to keep releasing secret(ish) stuff like that in updates or something. Gosh darn do I love this game.