Unshelled Koopa
A Beach Koopa is a Koopa Troopa that has lost its shell and wears nothing more than an undershirt and boxers. In Super Mario World, the Blue Beach Koopas will kick shells they come into contact with. The Yellow variety, on the other hand, will go into the shell. Instead of emerging as a normal Koopa Troopa however, the shell will begin to spin wildly and flash different colors. Beach Koopas were also found in Super Mario World 2: Yoshi's Island and Yoshi's Island DS, although here, they walked upright when evicted from their shells, instead of on all-fours.
In Super Mario 64 DS and Super Mario 64, Mario or others could jump on a Koopa Troopa to knock its shell away, transforming the turtle into a Beach Koopa. If attacked again, the Beach Koopa would be destroyed. If not defeated, the Beach Koopa will frantically attempt to dive back into its shell. Interestingly, Mario can ride on this green shell.
Appearances in Other Media
In the Super Mario World episode "Fire Sale", the silent, Koopa Troopa henchmen of Kootie Pie Koopa is continually knocked out of his shell in the episode, usually during one of Kootie Pie's violent temper-tantrums.