Dr. MacDeath is the main antagonist of the thirty-ninth book of the Give Yourself Goosebumps series, Scary Birthday to You!
He is a horror-themed party entertainer who is known to do horrible acts during children’s birthday parties, such as twisting kids into balloon animals and making party games deadly (such as using actual bombs during dodgeball and using a paintball gun filled with corrosive acid)
In one ending, it’s revealed that Dr. MacDeath’s job as a party entertainer is actually part-time during the summer, and his real name is Dr. MacDermott and his full-time job is being a school principal.