lord peach
A role reversal of sorts for the concept behind Bowsette: Princess Peach is transformed into a look-alike of the King of the Koopas.
As there is no set item for the transformation, it varies depending on the artist: depictions include a Bowser-themed Super Crown, a spiked shell, and a spiked collar similar to one he typically wears.
Lord Peach is usually depicted as a pink-skinned koopa, retaining her blonde hair and blue eyes as well as white gloves. There have been cases where he instead remains human like Peach, becoming a bishounen prince while gaining pointy ears as well as Bowser's red hair and shell. Whether the character is a genderswap also depends; the two main versions have Lord Peach either remain female but with a Bowserlike body, or genderswap to male.
Alternate names for this form are "Peacher", "Peachzer", and "Peazer".