yeah I always felt SOTN should of made it required to beat all the bosses before having access to the final room in the inverted castle, it's cheesy skipping any of them.
well anyone planning on it? on youtube would be nice.
here's a good start if you havent unlocked SOTN yet.
Unlock SOTN -
http://youtube.com/watch?v=qfP0IlQ8VAw