Billy Becker is a minor character who appears in File Under: 13 Suspicious Incidents, in the twelfth incident, "Troublesome Ghost."
Billy Becker was originally a stagehand at the Stain'd Playhouse with Hans Mann; the two of them notably would split the train set during Look Out for That Train Wreck so that the audience couldn't see.
After the closure of the Stain'd Playhouse, following the economic collapse of Stain'd-by-the-Sea, Billy Becker moved into an old shack in what used to be the Anchovy District, spending his time trying to catch rats in an old pillowcase.
Troublesome Ghost/Train Wreck
Billy Becker grew tired of living in a shack, and used leftover special effects from plays that had been performed at the Stain'd Playhouse in an effort to scare Old Lady Mann, who used to run the box office, out of her mansion. Using chains from Look Out for That Train Wreck, he would make a clanking sound, and leave rats in pillowcases under her bed to simulate rustling. He used her husband's old costume from The man who Looked Somewhat Like Winston Churchill to make a fake ghost, lifting it with wires they used on Dame Sally Murphy.
Lemony Snicket, Hans Mann and Jake Hix later found Becker hiding in a distant laundry room in the Mann mansion. He confessed to his plan, but Old Lady Mann took pity on her former coworker and agreed to let him stay in the east wing of the mansion. Together, they would sing and play harmonica to old Playhouse musicals.