some juicy muzzle fucking :3

Have meters or something available which will ultimately determine the subject's fate, will they choose to leave, will they choose to be your pet, or will they choose to stay and live there?

Some may find this as a turn-off.

this is so that furries/people can make the char look almost like their fursonas

Similar to tentacles, urethral sounding, cbt, and oviposition, often but not limited to, a penis. The tentacles or whatever jam in through the urethra and you can see them distend through the urethral canal all the way through in to the ballsack as they play/squeeze/eat the testis.
This fetish often interplays with internal views of anatomy and whatnot, everything from cross-sections inside the penis, to x-ray views inside the ballsack.
Could be fun considering it's also a cross-section of a lot of fetishes.
This fetish also uses maggots or insects, which I am not a fan.

Using saline to increase size of genitals and other body parts.

You have a subject sitting in a suspended box, and their junk is peeking out through a hole in the bottom. Do whatever you want to them, and based on what you see happen to just this little bit, make guesses about their: species, kinks, sexual stats, etc. The more accurate you are, the better the reward!

Basically a set of machines that the player can strap themselves or others into to run an automated experiment.

and the legs/butt proportions are strange, the butts always look flat, and the legs look too skinny