Tentacles are probably one of the harder things to rig, mostly because it is so dependent on exactly what you need the tentacles to do.
I can tell you right now that it is something that I still have not accomplished to any degree where I have been satisfied with my results.
Some people have created pseudo dynamic rigs that use posemorph to pass keyframed animation through to a rigged solution.
Others set up Spline IK so that they can create smooth animation using fewer controllers, in fact you can even blend a few methods together..so spline IK for the base and then a smaller IK setup for the tip for extra control.
Some people even use something as simple as the wind deformer (with falloff) to create the waving motion, and others still will actually drive the joint rotations to cause a wavy motion.
As for the video you linked, it comes from probably one of C4D’s most talented TDs, and I can’t be sure exactly how he set his rig up, but it probably involved some combination of what I have mentioned above.
