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Mutant Muck Monster is the toy Arthur gets from Grandma Thora, in Arthur's Toy Trouble. This toy was bought at David's Toys and was found in the bargain bin. The cost of this toy was $6.47, but Freddy K. said it was only $5 after 10 years. Which means the toy was probably only worth a 💵. The toy was a defect, and Arthur, Buster, D.W., and Muffy thought it is worth 2 million dollars!