Cool! It looks like a big version of the minifigure scale octopus that came in some of the diver serieses!
This was such a fun piece to build! I believe we did it in 2012...and it was adopted by members of the Chicago Area LEGO Users Group when we retired (so, folks still get a chance to see him on display from time to time!). Four of the tentacles were VERY articulate, two were quite flexible on the flat plane...and the back two were directly behind the head (and fixed) for balance. Enjoy!