My choices would be either:
Himiko Toga as either a Ludmilla-esque Dragon/Kaiju or cow (Himi-cow)
Or
Saiyan Saga Chi Chi as a Mule/Donkey or cow

Alien Force/Ultimate Alien Gwen turning into a Big Butt Donkey

Megumin from Konosuba becoming a dragon because of a failed attempt to cast her Explosion spell, starting with the tail "exploding" out of her.

Himiko Toga as some kind of insect or dragonesque Kaiju (Anguirs comes to mind)

Alternative Himiko Yumeno into a dover or a while tiger.

Nami or Robin as a crocodile (Maybe one croc one aligator)

Komi could become a journal of sorts with each page expressing various words like she usually writes down.

Mako as a setsuku style outfit for Ryoko.

And honestly something with Azumanga Daioh would be neat, but I can't quite get a full species or object kit for that.

I have more but I Dont want this to be to much!

I'd love to see Selena from Fire Emblem Fates turning into a fat pig and maybe getting fucked

Here's a few out there ideas I don't think I've seen anyone ever do before:

- Shion from That Time I Got Reincarnated as a Slime being turned into a bull from eating her own cooking
- Nala from the Lion King, in a twist, finding some Sandstar and becoming a lion girl that would look perfectly at place in Japari Park from Kemono Friends
- Ariel (mermaid) becoming a housecat
- Medusa and Pekola from Dropkick on my Devil becoming cows after drinking milk delivered by Minos tainted by Jashin meant for Yurine
- Amanda from Reincarnated as a Sword being accidentally turned into a Darkness Wolf after trying to examine Teacher

I think that's everything I can think of at the moment.

You know what would be great that I don't think anyone's done? Colette from the Disney movie Ratatouille turned into a rat