Very similar to previous makes from @Reaver but another great use is making tails (for skaven or what have you)
Start out by taking a small pea size ball of greenstuff.
Roll it out into a small sausage, giving it a slight taper.
Use the back of two plates to taper it more until you got it at the desired length.
Use the large plate from the small tentacle makler set and roll the tapered greenstuff between the plates, grooves aligned the same way.
Then, very gently, smooth out the beads made by the tentacle roller and add a sharp tip to the thinnes bit of the taper.
Lastly you can add some twitst and bends to them to make them look like tails and add that dynamic movement to them.
EDIT: Oh and a little trick @Admiral has tought me… these thin tips can get very fragile, coating them in superglue after the GS has cured makes them a lot more durable!