Twincup is the name of the pairing between Hiccup Horrendous Haddock III, Tuffnut Thorston and Ruffnut Thorston from How to Train Your Dragon. It is not a popular ship in the Big Four fandom, but there are still those who support the relationship. As one of the more unorthodox pairings, this can be considered an amalgam of Ruffcup, Tuffcup and Twincest.
In the film, Ruffnut and Tuffnut join in Snotlout whenever he is out to ridicule Hiccup, only to join in as Hiccup's fan when he begins to excel in dragon training. After Hiccup's secret is revealed, he gathers everyone in his plan to save the village from the Red Death, and eventually became members of Berk's new Dragon Academy.
Many fans liked to pair Hiccup with either Tuffnut and Ruffnut for differing reasons, and eventually these pairings would join together, the twins usually fighting over Hiccup's companionship, and would gang up on the scrawny Viking on this issue.
Note: Please add only ones that are part of the RotBTD fandom