In the episode, Bowser, through the use of a pendant, gained the ability to use Power-Ups, including Frog Suits. As Frog Koopa, Bowser would be covered in a skin-tight, green Frog Suit with webbed hands and feet; the "head" of the Frog Suit would also have menacing eyes and teeth.
As Frog Koopa, Bowser could swim through water several times faster, breathe underwater and jump long distances. Bowser may have also gained increased strength as Frog Koopa, as evidenced by him being able to kick a submarine with enough force to beach it ashore, only doing minimal damage to his foot in the process.
Bowser eventually lost the ability to transform into Frog Koopa when the pendant that allowed him to do so overloaded and exploded, due to being used too many times in a row.