Nheastvan,
A "bed" of 8 tentacles or so shouldn't be too hard to do with green stuff. The head could be attached on top (also with green stuff) once the details on the tentacles are done.
To make things move along a bit faster with the rest of the figures, I would make a quick push mould of the "bed" of tentacles before adding the head. Insta-Mold or just plain latex might work and then just press in green stuff to make replicas.
Thoughts?