Gothitch (also called the Dark Duo or Anti-Jackunzel by some) is the name of the pairing between Mother Gothel from Tangled and Pitch Black from Rise of the Guardians. Overtime, they have become an incredibly popular duo in the fandom.
Both Pitch and Gothel are the most often used antagonists in the fandom, acting as the "Bonnie and Clyde" of their kind.
They enjoy blackmailing the others with Rapunzel, preying on Hiccup's self doubts and trying to get Jack to join their side (although Pitch tries harder than Gothel). Gothel holds much emotional merit towards the group's adhesive Rapunzel, and could easily tear the group apart through her alone. Pitch's knack for sniffing out and picking at the fears of others could land the final blow (or at least seperate them temporarily), where they could make easy prey for the Red Death and Mor'du.This would make them a valuable combination on both a strategic level and to a personal level against the Big Four.
However, with ambition comes doubt, as both Pitch and Gothel's scheming personalities may lead to the two holding little trust in each other, one expecting (or attempting) to backstab the other. Sometimes however, Pitch and Gothel can have a romantic relationship.
Though the idea of a romantic relationship between these two is seldom touched upon, the chemistry between the characters has been tried at nearly every angle. Both (by different means) possess a level of immortality, allowing a long, complicated history to unfold. Fanfiction writers percieve Gothel as a witch or is associated with that kind of community, so her experiences would allow her to see spirits like Pitch, Jack, the Guardians and so on. Some fans even go so far as to compare her to (or even put her in the role of) Pitch's long dead wife Lady Pitchiner. Mavis Dracula is sometimes portrayed as their daughter.