Weird, labotomized chihuahua from the comedic animated series Invader Zim (2001-2002). It's known only as "the Spooky Chihuahua," otherwise nameless. Even the evil Commander Zim fears the thing, and due to having fled from its presence screaming "Madness!" fans to bestow the name Madness on the dog, though a couple episodes he's called Meat Dog.
Nickelodion cancelled the series partway through its second season, as the critical praise was not matched by viewership. The pilote plus 46 "canonical" episodes were issued on dvd in 2006. Several more unfinished episodes (possibly seventeen) were in production when the series was shut down.