I enjoyed the challenge, though I did use a lot of food up to beat him.
My strategy (once I realized what I was supposed to do) was upping energy shot and speed, going in front of him till he opens his mouth and shooting.... I could do this about 3 times in a row before he did the darkness + squid + shooting thing, at which point I retreated to a little nook in the tunnel, switched to sun form and went back in after he finished shooting, lit stuff up, switched to energy form, took out the squid and went back at his mouth.
Don't remember how many times I had to go through this sequence, but it didn't take very long. And I only got caught by the tentacles once or twice because I have a horrible reaction time.