It is first encountered after the Hero of Brightwall and Sir Walter Beck wash up on the shores of Aurora and make their way into a cave, where they find themselves fighting the Crawler's legion of "shadow children" as the Crawler itself taunts the two, especially Sir Walter. Moments later, the Crawler abducts Sir Walter, forcing the Hero to find and rescue him, fighting more of the Crawler's progeny in the process.
Later, the Hero of Brightwall learns that the Crawler is responsible for decimating the City of Aurora, killing many people, and that his/her older brother, Logan, previously crossed paths with the Crawler and was traumatized by the encounter.
After the Hero takes the throne of Albion from Logan, he/she learns from Theresa that, in one year's time, the Crawler will execute an attack upon Albion, and that he/she must prepare for the coming assault.
A year later, the Crawler comes to Albion, as Theresa said, and begins attacking. The Hero of Brightwall leads his/her allies in battle against the eldritch being, who then possesses Sir Walter. Thus forcing the Hero to fight his/her friend and mentor. He/She finally defeats the Crawler by killing Sir Walter.