@MrMario:
I got ya! I kind of had a feeling that might be what you were talking about. That room is part of the path that leads to boss. Seeing as you've already pounded the red one, it'll be lowered already.
To get down to that floor, you need to hit the blue pound block. (There's essentially three colored pegs to find, blue/red/purple and all three need to hit to make it to the boss). To find it, walk through the left wall on the first screen of the dungeon, take the stairs and go through the side-view area. When you come up, kill all foes and go right.
Now, go one screen up from the dungeon entrance and enter the blue portal.
Edited by Obderhode, 12 September 2014 - 03:27 PM.