From Homestar Runner Wiki
The Gremlin is a 1973 AMC Gremlin that was first used during the flashlight story in Homestarloween Party as The Goblin's car. During the story, Bubs claims that the Goblin "jacked it up on some fat tires, tuned it up on some 4.11 positrak outback 750 double pumper Edelbrock intake bore over 30 11-to-1 pop-up pistons turbo jets 390 horsepower", and even added a flux capacitor from the Back to the Future movies. It was then thrown off-screen by the Visor Robot, but ended up relatively unscathed. After that cartoon, none of the customizations were ever seen again.
It appeared in Where's The Cheat? in which Strong Mad turned it over in his search for The Cheat, only to find the Goblin. It was then again used in Dangeresque 1: Dangeresque, too? as Dangeresque's car, despite its obvious inoperability. In Main Page 19, the Gremlin appears when one mouses over the "Store" button. It also made an appearance in the Senorial Day holiday short, mostly to give Senor Cardgage's commercial a hint of "car sales" flavor, despite the event having apparently nothing to do with selling cars per se. According to road trip, the Gremlin has an eight-track player, and its windows and doors are broken so that they cannot be opened from the inside. After that cartoon, it is hinted that the Gremlin might be in working condition, and the reason that Strong Bad is unable to drive it is that when he got the car, the keys were not included.
In the action-packed credit sequence of rough copy, it appears that Strong Bad has gotten the Gremlin to run. However, this may be confined only to action-packed credit sequences. Bubs was seen behind the wheel of the Gremlin during an Easter egg in Blubb-O's Commercial, but it was sans tires, and standing on four cinder blocks. It also appears in Strong Bad's Cool Game for Attractive People, but is referred to as simply "Cool Car" (or "hot car" in Baddest of the Bands). In Dangeresque 3: The Criminal Projective, it plays the part of DangeCar-esque and has an auto-pilot. Oddly enough, in the next episode of the game, Strong Bad also calls it "DangeCar-esque".
In Strong Badia the Free, the Gremlin became two countries, Frontzeatserland and Hatchbackistan.
It is likely a Gremlin X, which was a sporty trim level available on Gremlins, because it has the body strip seen on those models.