SOLVED. Childrens book (most probably) about a man who either turns into a rollercoaster or finds out he's been a train all along. I saw a review of it here on Goodreads around 2014-2017ish. [s]

[Akela]

I think it was a popular one making rounds on Goodreads. I think it was one of those low rated crack books which reviewers like to read just to make fun of. The basic plot was about a guy who either gets magical train powers or discovers he's a train and it had an horrifying existentialist aspect to it. Possibly body horror but I'm pretty sure it was a children's book.

[Banjomike]

That sounds like "John Duffy's Brother" by Flann O'Brien.

[Rainbowheart]

John Duffy's Brother for Banjomike's suggestion.

[Akela]

No I'm sorry this isn't it. The one I am talking about had a Goodreads summary and at least one review by a popular reviewer if that helps.

[Emma]

Twisted by Miranda Leek?

[Rainbowheart]

Twisted! for Emma's suggestion.

Also kinda reminds me of that thread about the boy turning into a gas pump, which turned out to be Super Giles.

[Akela]

YES! That's it!!!! @Emma Grahl thank you so much I had been looking for it for a while! I can't believe how fast I got an answer you all are miracle workers
@Rainbowheart please move it to the 'solved' section. Sorry I mistook rollercoasters for trains, I suppose there's no way to change the description now, is there?

[Banjomike]

I've added some info to the author page including a link to her website which has some images from the book. It does look like an interesting book but the sequel does not appear to have been published.