The Ark has everyone's DNA, there's a hidden mirror they find that uses the database's DNA and determines how you look 100s of years from now. It was deemed too disturbing, or caused obsessive problems which is why it was hidden away. Roddy and Thax think it's fun at first, but the mirror reacts very differently to changelings like Leaufonz.

Changelings aren't really Shee. At all. They're amalgamous Alien genetic material injected with Shee DNA to take on Shee shape. Changelings don't age naturally. So the mirror portrayed Leaufonz as he really is, with horns grown out (he shaves them down). It's the greatest nightmare for Leaufonz, bc he hates being a changeling, so something like this blasts through all his denials and every future he sees for himself as a "shee". TLDR Leau has always had major identity crisis. In the dream he thinks there's a mistake, because the Ark collects your DNA data as you are spliced, and Changelings aren't allowed to splice (for prejudice reasons, but formally it is stated bc "they can already reproduce naturally"), and Leaufonz was born. So they go through this minor adventure where they find our Leaufonz's DNA is, in fact, inside the Ark's database from other stuff, and it solidifies Leau is and never will be a Shee in any capacity other than heart. (edit: the others already know, it's quite clear, but Leaufonz just needs that physical evidence for himself he's so deep in denial)... but along the way they realize being a Shee doesn't really mean you have to BE a Shee afterall. Even if Leaufonz still has his identity hang-ups about it.

It was cute, but also really sad. I think a lot of us can feel that way towards certain stuff in our lives and like Leau, you never really get over it, not entirely.