Baron Petri von Honeydew is Dr. Bunsen Honeydew's recently deceased uncle from the 2000 Muppet PlayStation game Muppet Monster Adventure. The Muppets accompany Bunsen to his uncle's "run-down old castle in the middle of nowhere" for the reading of Petri's will. Bunsen says that Uncle Petri had quite the flair for dramatics.
As the Muppets arrive at the Baron's castle to hear the reading of his will, Robin the Frog faints. When he regains consciousness, he learns that his uncle Kermit, Miss Piggy, Fozzie Bear, Gonzo and Clifford have been turned into monsters. Robin goes on an adventure to restore his friends' souls, ultimately fighting Baron Petri von Honeydew as the final boss.
When the Baron is defeated, Robin faints again -- and when he comes to, he finds that he's fallen asleep, and that his adventure was a dream. As Robin tells his friends what he dreamed about, a painting of Baron Petri shushes him -- hinting that the events of the game were more than just a dream.
The Baron's name is a reference to a Petri dish, a common piece of laboratory equipment for biologists studying cell cultures. The Petri dish was named for Julius Richard Petri, a late 19th century German bacteriologist. It mirrors the fact that his nephew is named after the Bunsen burner, another piece of laboratory equipment named for its German chemist developer.