I guess at least some of you have noticed that some platforms in the last Bowser level have Goombas and Koopas as a wall texture. (To be honest, I didn't.)
But did you ever notice the textures on the pillars on the topmost platform of this level?
And by the way, if you look behind the wall in the castle room that leads to cool, cool mountain (easily done by standing near the wall ,pressing C-Up and rotating the camera) you can see a floating letter. The American version got a F, the European one got a U and the Japanese one got a N. FUN!