I've made several of these octopi, but this is the biggest so far. It measures 42" across, using a 10mm hook and 2 yarns together - Bernat Blanket and Bernat Baby Velvet. I have to make another one using the same yarns, but I'm going up to an 11mm hook so it will be even bigger!! This is like a crystal octopus, which changes from red to teal when it needs the camouflage in greenish surroundings. Look for a You Tube video of the crystal octopus changing colors. It's pretty awesome!
I use glass cabachon octopus eyes - a pricey choice, but it adds to the realism. These are also available in purple and orange in a variety of sizes. I used 30mm.