Is there a way to remove a specific body part from the creature file? Let's say I want a creature to have two heads, one with ears, the other without. I'd like to avoid messing with body plans though. I could create new body parts, but I want to keep it to one file.
You will likely need to create new body parts or alter existing ones, and set it up so that one head can be given ears and the other cannot. There isn't a tag that basically tells the part to only apply itself once.
I posted a separate thread, but thought I might also inquire here where there is more activity; but a generic 'have you ever encountered' kind of question, regarding added/creature_variation'd animals having duplicates in game, the second pairing of which crash the game when they appear or created in arena mode. Maybe someone' encountered that before and has some experience with the nature of the cause?
There are a number of reasons why a creature could crash the game. Could you post the creatures in question? It would help if we could see them and potentially help spot errors.
At the very least, I can say that a creature-variation may not alter the variated creature's name automatically, and it may need to be defined, otherwise it will use the name of the creature it is based off of.
How do I get a creature to randomly generate, similar to FBs/Titans?
In short, you can't. Though there are utilities that can create random creatures.
Or you can attempt to replicate randomness by making a single creature with an incredibly wide variety of castes.