My First mold so be nice!
The only problem area is the ''waving'' tentacle so I would suggest making it out a strong but flexible rubber.
I'll leave it up to you guys to experiment with it!
Made in TinkerCAD using the MakerBot's file.
Print at 0.2 resolution and with support to hold up the top of the head.
Once printed smoothing and sealing with Acetone works well and makes it somewhat watertight.
Line up the blocks and push or pour in the material. I held mine together with elastic bands but you could seal around the edges with something if yours leaks.
I made mine out of air-dry clay which was obviously too fragile and stiff but it was only for a test.