That's right, 2 years after its release and probably a little under a week of actual design you can now play Penguin Peak B-Side. If you though the normal game was too easy and wanted something harder, more unfair, and less playtested this is just for you. Even though it's just a different (and much smaller, more linear) map, it uses a bunch of weird tech and exploits that wouldn't really be fair to put in the main game, and you even get the upgrades in a different order, so you might find some neat and new uses for the mechanics.

Installing:

Just download/extract the b-side zip, and replace the res/maps folder in your version of the game and you'll be good to go. There's also a pretty helpful readme in the zip as well that explains things in more detail, and has some usefull tricks and tips for when you get stuck. I'd recommend giving it a look before/as you play.