Please see Carthus Sandworm instead
Disabled huge *****er of a crossbow, then ent down. Used yellow bug pellet, after worm's first electric attack, i got up close. His electric attacks did no harm when right next to him, at least when by the furthest protrusion of his body to you when you run straight at 'em from bonfire shore. He never hurt me when he moved either. Then, to be safe n see what happens, i seem to have been able to roll underneath him and attack from inside his coiled body, which, by the way, is far doper and looks far djfferent than from outside--he seemed to be somehwat of a skeleton, you'd see what i mean. Anyway, hack away from here. Done.
kill the worm from where the ballista can't reach you, it'll just stay there after you leave
Once you're not being shot at, you can just stand right in the area where the ground switches from lake to stone. The worm will coil in front off you and you can poke it a few times before rolling away. Rinse and repeat.
Stand on the ledge and kill it with ranged. Super ez.
Killing the sand worm gives you 6000 souls, lightning stake, and an undead bone shard