Mavcup is the name given to the romantic pairing of Mavis from Hotel Transylvania and Hiccup from How to Train Your Dragon. The ship is not widely popular around the fandom, but it does have several followers.
Mavis and Hiccup both face problems of having to prove themselves to their fathers, who are either overprotective or disapproving, respectively. Much like Mericcup, the pairing may often be portrayed as a Romeo and Juliet type of relationship between a vampire and a human Viking, where the two groups are at a feud with one another. Mavis, as the more energetic and outgoing of the two, would most likely initiate the relationship and might find Hiccup’s sarcastic attitude cute and funny. As an adventurous spirit, she may also enjoy flying around with Hiccup and Toothless.
The pairing most likely resulted from the Spectacular Six, but fans generally prefer to keep it separate.