The thing about killing 256 Necrophobes is false, I read. From what I know, all you need to do is kill all the Necrophobes in the Leo Gate Stone area, and then keep going from that area to Waystone XIV. Just do that until the Larva Eater appears in the Waystone XIV area. And maybe getting the highest chain level is good, too? I mean, just getting the Larva Eater to drop something is hard, so you'll want to have the highest chain level to improve your chances of getting good items if it drops something. If you kill the Larva Eater, and you don't have a Danjuro, go two areas away form the Waystone XIV, but make sure to do it by passing through the Leo Gate Stone so that you don't accidentally respawn the Necrophobes that you killed. Do that, and then repeat the the going from Leo Gate Stone to Waystone XIV thing until it respawns again. You can actually chain the Larva Eater this way. I read this somewhere, and it worked for me, but I was never patient enough to get a Danjuro. Good luck.