Hello,
I was wondering if it is possible to create the water tentacle like the one in the movie Abyss?
Any advice would be appreciated
Thank you!
It should be possible, i never did it but with some procedural textures, softbodies, transparency or liquid simulations it should be good. I am just guessing 
Still or animation? Still would be extraordinarily easy. Animated… not as easy.
There is an example of a tentacle built with an array modifier (including a sample .blend file) on the wiki:
http://wiki.blender.org/index.php/Doc:Manual/Modifiers/Objects/Array
You could try to put a whole bunch of metaballs on a spline with dupliframes.
It would be totally possible. A very nice looking, but maybe not TOTALLY controllable or fast possibility would be fluid control, a great feature of blender that combines fluid simulation with any animated mesh.
Another option would be using a regular mesh with a chain of bones, (or a ‘bones on a curve’ armature) controlling the tentacle, and your face and head controlled by a regular face rig, and then your mesh altered by a ‘displace’ modifier set to use an animated procedural texture.
Obviously material would go a good deal into this effect as well, but that’s an entirely different subject which might be better tackled once you have the physical side of your effect down.