When the Quacken attacks, its tentacles don't all spawn at once, with several of them spawning only after brief delays. If while the tentacles are spawning the player saves, quits, and reloads, the spawning event doesn't restart, leaving only a few tentacles spawned and the Quacken largely vulnerable.
Steps to Reproduce
Cause the Quacken to spawn and/or move to a different location, and save, quit, and reload immediately after the first few tentacles surface.
Cause the Quacken to spawn and/or move to a different location, and save, quit, and reload immediately after the first few tentacles surface.