And I don't think the book is canon.

Imagine if the villain is an Ogre

it could be most likely Peter Pan.

I think the villain could end up being the Troll from the 3 Billy Goats Gruff story since trolls are usually green

Or it could be an Ogre. Maybe Shrek's Father or Brother

Late here but imagine if the villain is himself, LOL.

They kind of already did that in the first one, I know there was Farquaad but Shrek started out as a lonley grump in the beginning who was rude and nasty to anyone because he wanted to be left alone

Nah Firestarthegodcat's onto something here XDXD

I think the villain should be Foxy Loxy or the Troll from the 3 goats gruff story (there hasn't been an animal or creature villain outside of the Wolf in PIB 2, all of them have been humans/magical beings)

@Thom7 Foxy Loxy would definitely not be the antagonist of Shrek 5 because he is actually an antagonist character from a 1943 Disney anti-n*zi propaganda.

Foxy Loxy is also from the original Henny-Penny/Chicken Little story, and sometimes called Foxy Woxy. I don't think the character will appear in Shrek 5, but I really doubt that that specific reason is what would hold back Foxy from appearing. Plus no one really remembers that propaganda cartoon anyway