Board Thread:Questions and Answers/@comment-25007558-20160115182629/@comment-37518581-20190424040108

That actually makes sense. In the final battle at the Monster hive, we don't see any of the other stolen costumes hung up or laying around anywhere. It would make sense that they were brought to life, but terrorized the city off screen. Otherwise, where else would the Masked Figure keep all the costumes?

Also, remember in the scene where Mystery Incorporated first enters the Monster Hive and sees the costumes hanging up on a farm next to the machine. Captain Cutler, Zombie and Miner 49er are on screen and acknowledged to be there, but then Fred states:

"they're All Here".

its obvious the rest of the monsters were implied to have been brought to life off screen.