this boss is pretty easy, but there is some catches
-be ready to mash if you get grabbed. mashing fast enough will prevent most, if not all damage
-be ready to run away if he starts vomiting. that acid don't do much dmg, but will break the durability of your weapon very quick
-staying in his lower side is the most safe position. Instead of attacking you, he will be constantly flying up to adjust himself and trying to fall on you. Keep your weight light and just run circles aroudn him.
-there is a special item (dragon axe) if you cut his tail off, but most of the time it's not worthy the risk of getting sweep by his tail. This weapon requires 50 of str to equip in 1 hand, and have zero scalling in all status. So you won't be using it early/mid game nor in ng+