For one of my current projects I needed a few Octopus Like tentacles. I had previously sculpted tentacles for one of my Dark Eldar conversions using floral wire and green stuff so I decided to take it to the next level.
Get a length of thin bendable green floral wire and lay it on your work surface. I use palette paper or wax paper. Make sure there is some moisture on the paper too. You'll see why in a bit.
Wrap the putty around the floral wire so that the wire becomes the center core of the soon to be tentacle.
Roll the tentacle in your hands until you get smooth tube of putty. Make sure you have wire edges poking out either end. you will need these in a few steps.
While wearing gloves, take the tentacle roll and put it on some wax paper. Make sure your gloves are wet to avoid sticking to the putty. Smooth the rolls into soft triangular slabs, making sure the bottom is flatter than the tops. Use a sculpting tool to even out the bulges that may happen on the sides.
Take a latex glove cut open or plastic wrap and lay it over the tentacles. Make sure there is a layer of moisture between the plastic wrap and the putty. Take a wire bristle brush and start poking it into the length of the tentacle randomly. this will add a porous skin like texture to the outside of the tentacle.
By now the putty will be semi hardened. Take a tooth pick and start adding a few ripples along the length of the tentacle for added texture.
At this point, this is what the tentacle should look like.
If your paper was properly moistened earlier, you should be able to lift the tentacles from it easily. At this point you'll realize the bottom is completely flat and smooth. You want this. Take the tentacle by the wire ends and bend it into a flowing shape with the flat end being on the inside. Once you are happy with the "flow" of the tentacle, set it somewhere to fully harden. I usually take the wire end and stick it into a piece of foam or something so it stands up.
Take tiny balls of green stuff and mush them onto the flat end in 2 columns running the length of the tentacle. Take the flat end of a small drill bit and push into the ball and voila, octopus suckers!
You may want to do this in sections, let them harden, then do the next section as not to accidentally mush any suckers.
Once you've sculpted all the suckers, it should look something like this.
Then you simply snip the wire ends off, putty the tips of the tentacle if needed and BOOM!
Here's the tentacles in action in one of my new builds.