So here's 4-7, the second Pwnhammer in the game, based on "Pwnhammer Duece" from Invasion 2. The Mother Brain fight becomes available after completing the Shadow Realm and it's the Key exit. Note that it's in its own sublevel called "04-07B" so be sure to test that too since in editor mode entering a level warp ends the testing. The key is in a secluded room in the main level that can only be accessed via the sublevel, to ensure the Key path will open in the world map. Please give feedback!
http://www.mediafire.com/download/kmbr8eoz1b3xqvx/