I tried a lot of times but I still can't beat it.

I watched some videos. People get close to its left hand and beat the crap out of it while they avoid its right hand attack and its left hand smash. I tried to do the same, but he keeps summoning that ghost tentacle even if I'm close to its hand.

I can avoid both right hand's attack and left hand's smash, but I still don't know how can I avoid the ghost tentacle.