so sorry for the late response anon!! i'm like. semi familiar with the princess bride (i've watched it a few times, nothing too recent though), and honestly the premise would make such a fun au! i love me a whimsical/fantasy fic. ;) not sure if this u was asking for advice or how i personally would do it, but in my case i think makyumjyo would lowkey make for a hilarious main trio (vaguely filling the roles of westley, inigo, and fezzik in that order). but also i feel like nikjju as westley and buttercup would just be classic asf. much to consider.

that being said. i have considered writing fics based off of existing works of fiction before, and i always find it more fun to use the original material as a general framework without necessarily copying it beat-for beat! playing around w/ characters and plotlines in a way that makes sense for who's filling the role can really make the story feel unique (as unique as fanfic based off of an existing story can anyway LMAOO). if this Was in fact you asking for advice, and this is a project you're considering writing, i encourage you to go for it!! i always love to see niche/unusual fic ideas in the tags, hehe. :))