Alright, so I've been going around my Fire Red rom replacing various Pokemon with 4th/5th gen pokemon. Totaled up to around 100. Got in all their sprites and icons fine. I've been making use of the 25 Unown slots between Celebi and Treecko as various extra mons.
Most of the Unown slots are evolutions of existing gen 1 and 2 mons in the rom. I can add in some of the evolutions fine, but adding in others somehow causes YAPE to crash. I have multiple Unown slots functioning 100% fine, but others are weird.
I have not tampered with the rom whatsoever outside of editing Pokemon and attacks, so I very much doubt I've overwritten something.
These "bugged" Unown slots are functional to some awkward degrees. . .I can go in and edit them if I go to them directly without going to an evolution. The current evolution table where I previously was stays, though, and I can't go to any other Pokemon after going to this Pokemon, having to close and reopen it. I also cannot make these bugged slots evolve themselves, even into "normal" slots.
Weirder still, I overwrote Celebi, a normal Pokemon, with a new Pokemon. Sure, it's right next to the Unown slots, but it should be normal, right? Nope, Celebi's slot is one of the "broken" ones. The regular Pokemon in the rom are fine, but yes.
One of the Unown slots even somehow has had random evolutions assigned to it, evolving into Entei and Beedrill somehow. They can be removed and this particular slot functions fine but it's weird enough that it's making me panic something was overwritten.
My best guess is something along the lines of there only being so many evolutions being allowed in the game and I broke the table by adding too many and/or the Unown slots just being really trippy. Looking for an explanation as to why this happened more than anything, pretty much assumed the rom is screwed.