I'm not sure if this has been found yet but...
oubliette hall
Enter the door after going up the elevator in the oubliette and look left, you should see two green glowy rock things, walk towards the one on the right and stand directly in front of it. Turn into the morph ball and double bomb jump, at the top of your jump push the dpad toward the rock and unmorph. Walk forward and you should automatically walk diagonally right, when you reach the corner turn back into morph ball and push toward the corner to stay there, whilst still holding the dpad double bomb jump and you should come down through the wall landing on the continued floor. From here you can jump to the right (making sure not to fall back through the wall or off the edge) there's not much you can do but you can bomb jump into the morph ball tunnel if you want.
I found it a while ago but I'm not sure if it's been found before, yeah
heres a video of it:
Enter the door after going up the elevator in the oubliette and look left, you should see two green glowy rock things, walk towards the one on the right and stand directly in front of it. Turn into the morph ball and double bomb jump, at the top of your jump push the dpad toward the rock and unmorph. Walk forward and you should automatically walk diagonally right, when you reach the corner turn back into morph ball and push toward the corner to stay there, whilst still holding the dpad double bomb jump and you should come down through the wall landing on the continued floor. From here you can jump to the right (making sure not to fall back through the wall or off the edge) there's not much you can do but you can bomb jump into the morph ball tunnel if you want.
I found it a while ago but I'm not sure if it's been found before, yeah
heres a video of it: