This is the area I got stuck before.. in the 1x1 black box.. If you figured out just spamming the buttons gets you through.. I am glad I figured it out; exploring the rest of the game was fun!
Oh yeah. There, the best strategy is to either fall twice into the level below and climb back up, or time a jump and switch to go through sideways. Difficult controls, but very rewarding once you learn the timing.