There's also Runes of Pandemonium from the creator of House of Pandemonium, I rather like it. Collecting different monstergirl forms and their abilities is a core part of the gameplay.
You must be registered to see the links
steam page, it's free
You must be registered to see the links
itch.io page if you prefer that.
https://f95zone.to/threads/4830/ The Last Demon Hunter has a bunch of transformation bad endings and a few transformations where you can keep playing the game as normal (catgirl, vampire, dragon girl, and a couple or so others).
https://f95zone.to/threads/42203/ Odyssey of Gianna has many transformations that can be inflicted on your party members, many are of the inanimate variety but there're a few monstergirl ones like orc, succubus, slime that you can level up and buy abilities for.
https://f95zone.to/threads/27513/ Crimson Veil has a whole bunch of monstergirl transformation bad ends, and there's one vampire route that you can start in the right spot (just do the delivery to a mansion quest that'll show up eventually) though that's not yet finished.