I have about 40 or more glitches from SMAS that I have tried to send to Deezer but it didn't go through. So I'll be posting them soon. This is all on the SMAS cartridge. I don't know if it would work on seperate games like for the GBA's SMB3 or whatever.
But for now I just found a glitch from SMW on the SNES.
In the first castle you will encounter a P-switch under the fence deal you climb on. Kick the P-switch straight up, hold Y, and quickly jump on the fence and let the P-Switch hit you. It will be stuck on Mario in the front. Since his back is to you, yu can see the P-switch overhang Mario's body. It ewill drop once you let go of Y.
SMAS glitches coming soon! 
"Yesterday, when I''m smaller..... I wanna fight that Mario the day before yesterday."