The first step, before I spent too much time thinking about and working on this, is to show the proof of concept. Specifically, the one part of this that I haven't done before and haven't seen anywhere online is to make a tentacle curl and uncurl by pulling on a wire. Assuming that works, it's easy to attach the wire to a servo and have that controlled by the Arduino.
This first picture is a small tentacle made as a simple chain (about 20 stitches) then a single crochet in each st going back with more tension and tied at the end. Because of the increased tension, this tentacle has curled all on it's own. That is the effect I am going for, only creating tension with the wire.
This is a longer chain (about 50 stitches) and again, I have done a chain and then a single crochet in each stitch to the end and tied off, but tried to keep the tension even all the way. I have then threaded a wire through one side of each stitch. You can see the wire sticking out at the top and I tied it off at the bottom. (Ignore the extra strands at the bottom, I couldn't be bothered to sew them in or cut them off just for this test).
I tried pulling on the wire and the tentacle did move, but not in the way I wanted. After a little experimenting, I realized a slightly curled tentacle will work better as a starting point. These 2 pictures are taken one after the other and I am using my spare fingers to pull on the wire. You can see that the tentacle has curled up very nicely just by pulling on the wire.
This is exactly the effect I was hoping for and I am getting very excited that this project could actually work and be easier than I was expecting. If I have 8-10 tentacles curling like that on the mask this is going to look awesome!
I also spent a little time seeing if the process is reversible, and this is a bit harder, I needed 2 hands to push the wire back in carefully in order for the tentacle to straighten, and it was difficult to hold my phone to take pictures at the same time. I can see where this is going to be a challenge in the final mask, but I think I can get it to work.
The next step is to set up a simple breadboard circuit to test if the servo can curl and uncurl a tentacle directly and repeatedly. (I think I will use the tutorial project on the Arduino site to control a servo from a potentiometer to give me manual control for testing). I will try to upload a video of that test as soon as I can. Then I guess I should get started on making the main shape of the actual mask and see if I can figure out where to include al the electronics and the battery etc.