Appearances on the show
In Take Elmyra Please, he invents a clean-burning fuel from cholesterol, after a huge explosion that blows the roof of the house and awakens Baby Duff. After the family calm Baby Duff back to sleep, he rushes down, now with his clothes blasted from the explosion, to tell them about his new discovery. His new invention becomes the subject of tonight's newscast, and word gets round to the rival fuel company, Happy Sunny Oil, owned by Arthur Jabba, who sends George and Leonard to the Duff house to capture one of the family members and hold him or her for ransom, so that he will have to surrender the fuel formula. With the help of Duncan, Arthur's plan has failed.
In Grandma's Dead, he decides to desalinize tears so he can turn them into drinking water. His first specimen for his new project is Elmyra, who is upset over her dead hamster, Jan Brady. Throughout the rest of the episode, he collects tears from various people. Towards the end of the episode, everyone toasts Elmyra's funeral with the freshly made drinking water, which tastes horrible and is spat out on the lawn. As it turns out, this failed experiment has a use after all; since tears are salty and salt iodizes slugs, the water makes the perfect slug repellant.
Appearances Outside of Tiny Toon Adventures
Mac has had several cameo appearances in Animaniacs. He can be seen in the audience alongside Amanda in the cartoon, La La Law, when the Meter Maid arrives to the courtroom. He can also be seen alongside Emily watching television during The Brain's broadcast in the Pinky and the Brain cartoon, Battle For the Planet, as well as alongside Baby, watching television during The Brain's broadcast in the Pinky and The Brain cartoon, Meet John Brain. Ironically, he did not appear in any episode of Pinky, Elmyra, and the Brain.