Not the Great Big Hen
Maths Mansion is a British educational TV series for school years 4 to 6 (9 to 11yr olds). It follows the adventures of "Bad Man" taking kids to his mansion, Maths Mansion. There, the kids learn and are tested on maths. They do not always pass the test, and this is shown in various episodes, one of them being Angleman!. Interrupting the program, is another program, about "Sad Man", who seems to be quite happy. He demonstrates math in songs, puppets, and games. Sad Man has a puppet called "Decimole", as for him being a mole. Decimole is known for attacking people. But, in the final episode, Bad Man digs up Decimole, and Decimole kills Bad Man.
Maths Mansion Wikipedia