>>397342637
https://www.youtube.com/watch?v=wT8fViZpLmQ
watch this video to understand how AimIK works. It's IK made for aiming gun arms at targets during other animations, but who cares it works for any number of bones pointing at anything during normal vrchat animations and movement. I'm only using AimIK for the last eight bones in the tail, which is probably more than you'd need for a tongue. Then slap on physbones to make it floppy, but not too much because it the phybones will cause delay and that means less control.

1. make a new object and constrain it's rotation to your avatar's hand, this is the object the chain will rotate around, the "pole target"
2. make a child object of the pole target and drag it "forward", this is the "aim target" the chain will try to aim at
3. find the last bone at the end of the chain and assign it as the aim transform, this is final bone the chain will try to have pointing straight at the target, the rest of the bones will bend progressively toward it. You might need to make a new child object if the blue axis of the bone isn't pointing towards the end.

It might be obvious but you probably want the pole target in your avatar's month and the aim target somewhere in front of it since you're only interested in rotation not location, but if you have a really long one maybe you want to go for a full parent constraint with an offset instead and "puppet" the end of the tongue idk do some experimenting.

You'll need FinalIK if you want to test it in the editor which will help immensely, but you technically don't need FinalIK to upload an avatar that uses it to vrchat, just the right guid stubs so vrchat knows to switch it on:

https://github.com/VRLabs/Final-IK-Stub