Mario's Pad

Visit #1

Upon entering Mario's Pad, you will have to jump off the wall. Run outside and talk to Toad, then try to leave. He will bring you back to the save box, then just leave again.

(video credit: Mill)

You will go back to Bowser's Keep, only to be thrown off the bridge. 

Do not enter Vista Hill. 

Go back to Mario's Pad. Run inside and talk to Toad, then try to leave Mario's Pad. You will bump into Toad and he'll give you a Mushroom.

(video credit: Mill)

Item Tutorial Skip: Choose option #2.

Timed Hits Tutorial Skip: Choose option #2

Choosing either tutorial is a significant time waster, and is basically a reset.

You will not come back to Mario's Pad unless you are doing Mario's Pad manip for Bowser Doors.

Visit #2 (if doing Mario's Pad Manip)

Save, and then soft reset.

Perform Mario's Pad Manip. 

Go to Bowser's Keep.