With this addon you can give some bones that jelly bounce. That is the easiest way to describe the addon in less words as possible. You might also call is soft body for bones. Use it for tentacles, bones, and everything that should give some lagging. The RigFlex addon does excellent work and is pretty simple to use if you know what it’s purpose.
How to use the RigFlex addon?
First animate your object with armature or some bones. Meaning; animate the armature in posemode. After that the RigFlex addon comes into play. Think what bones should lag, for example few end bones of a tentacle. Then you select those bones in Pose Mode. And then you open the N-panel, Open the RigFlex menu and press Bake. Play the timeline and see the bones lagging. If you got that, you saved some time figuring out what the addon is good for.
Where to download the RigFlex addon?
You can download that addon at Github. There you see the green button on the top right and you choose for Download. One you downloaded the zip-file, open Blender > Edit > Preferences > Addons > Install. Navigate to the zip file and press Install.
Where can I find the documentation?
If you already went to Github to download the RigFlex addon, you must have seen the documentation as well. In the documentation there is some more information about the Changing the stifness. (Yes, the bones are pretty stiff per default). Also a not about Freeze and Unfreeze features.
Quite a unique addon I believe. And really useful to give some parts of the animation with bones a natural look. You could do it by hand, but this must look way better. Thanks to nerk987 on Github! I will keep this addon not only on my harddisk but also in Blender.