In this form, Leon normally wears a shell over his diaper. However, he can remove the shell and use it like a snowboard. He can also use the shell to protect himself from attacks that he normally couldn’t block.
Unfortunately, if Leon gets hit while riding his shell, he’ll temporarily lose it. Furthermore, while Leon’s other forms can swim (loosely, most of them, his diaper absorbs lots of water and prevents him from doing anything besides dog paddling), the Turtle form can’t and just sinks to the bottom.