It seems many people are confused about how to find the Abyssbat. Here's how: First, go to the northwest Ruins, or Ancient Ship as it is also called, in Shingrow. From the entrance, go into the ship and take the back path. At the back wall, examine the vines to open a secret door. If there are enemies, fight them, leave the room where you came in, and re-enter. Keep fighting the enemies, leaving, and re-entering until there are no enemies when you enter. If this is the case, you will be attacked by the Abyssbat as soon as you take a step forward. Good luck, he's tough.