The Cheese Monster was a large male humanoid made out of yellow, oozing cheese.
It was monstrous and very menacing; scaring people who got in the way.
A Pup Named Scooby-Doo
The Cheese Monster's first act was to scare away all the employees from the factory. He declared, "No more Scooby Snacks!"
The gang wanted to help the owner solve the case and investigate inside. They soon found it while searching in the cheese lab and it chased them into a dead end on a catwalk. When all was lost, Velma Dinkley saved them by using her yo-yo to pull down a lever on a control panel activating mechanical hands picking each of them up and away to safety.
When they split up, Velma, Shaggy Rogers, and Scooby-Doo inevitably walk right into the Cheese Monster's path. The trio play him for a fool and get him to do an interview for a job there by filling out dozens of forms. They make this their cue to leave for "lunch", infuriating the monster.
When the kids reunited they found and interrogated Boris Roquefort who was sneaking around. Eventually he had enough and ran away, and the gang followed. They ran into the Cheese Monster and a colourful chase scene ensued. In time, the Cheese Monster captured all but Scooby. Scooby found them being tied up by the monster, scaring him away, only to bravely return when he heard Shaggy crying for help. The gang's only hope was for Scooby to save them now, but Shaggy thought he was too chicken, a coward, a fraidy cat, etc.. Scooby caught him, disappointing him. Shaggy was thrilled that Scooby returned without a Scooby Snack. His cheer was cut short though, by the monster who chased Scooby around the room. Daphne had had enough and wanted to leave because her skirt had been wrinkled so she cut through the rope with a nail file. Meanwhile, the monster chased Scooby into a small room, the door closing behind them.
Scooby was now trapped with the monster and the gang couldn't get in. They heard slurping noises from the inside and feared the worst. They're shocked when the door bursts open; a man running out in his underwear, his costume having been reduced to the mask still covering his face. The kids found their puppy greatly fed from consuming most of the monster's costume and congratulated him for his achievement. Velma used her yo-yo one last time to catch the bad guy, tangling him by the ankles, sending him crashing into the floor, head first. Shaggy said they should call the police so they could "grill" this Cheese Monster; Scooby was quick to laugh, but really doesn't understand.
The gang called in the owner, and a policeman now had the bad guy underneath the Cheese Monster cuffed. Now that the monster had been caught she could re-open her factory, but they still didn't know who was underneath. So the gang reviewed the clues: A document containing a secret missing formula and a blue suit. There's only one person who would want to run the Scooby Snack Factory out of business and that person was: Larry P. Acme, owner of the rival dog biscuit company, Acme Dog Biscuits. Without the competition, his company would supply the stores taking over the market, and he would've use the stolen formula to improve his own dog biscuits making them a huge success. And he would have gotten away with it too if it weren't for those pesky kids and that puppy who ate his costume! But it was delicious!