The Head (TV series)
The Head was a MTV Animation series, airing 1994-6, that's beloved by Lawndale High student "the Head". It was created by Eric Fogel, creator of Celebrity Deathmatch and director of multiple Daria episodes.
The Head is the story of Jim, a trade-school student in New York City who awakens one morning to find that his cranium has enlarged to mammoth proportions. A week later, out bursts Roy, a little purple alien with an odd sense of humor who has taken up residence in Jim's head. Roy needed a place to stay to adapt to the Earth's environment while on a mission to save the world from a power-hungry alien named Gork.
Aiding Jim and Roy are Jim's girlfriend, Madelyn; his personal physician, Dr. Richard Axel; and a group of "human anomalies." The group consists of Ray, a landscaper who has a lawnmower blade lodged in his skull; Mona, a beautiful young woman with a short tail; Ivan, a Russian who has a mouth in his chest; Raquel, who has an enormous nose and buckteeth which give her a slightly ratlike appearance; Earl, who has a fishbowl in his mouth; Chin, a long-limbed former freak show performer from China; and the annoyingly normal head of the group, Shane Blackman.
While in real life, The Head didn't have T-shirts of it, in the world of Lawndale it did! "The Head" wears one as a nod towards Daria's sister show.
Is the Head real in Daria's world?
If you asked Glenn Eichler, "no".
However, in the first episode, Butt-head appears for a few moments to deliver a VHS tape to two federal agents. He is quickly relieved of the tape and booted out of the van. (How Butt-head got to New York City to deliver the tape is not explained) Thus, The Head is technically, possibly, maybe in continuity with Daria!
As few fans have seen the show, we have rarely seen anyone outside of The Angst Guy try to make this argument or use The Head for fanfiction. TAG used elements from The Head for his unfinished story "JÖRMUNGANDR".