A dancestor is a player's ancestor on one side of the Scratch, but is also a descendant on the other side. This brief explanation is from the MSP Wiki, and it's about all I can give Ты right now. An example of a dancestor would be Kankri Vantas, who is Karkat's dancestor. I'm not sure if this is correct, and please tell me if it's not, but dancestors exist in a different session of the trolls, and they are counterparts of each other, или Pre-Scratch (dancestors) and Post-Scratch (trolls). Ancestors are a bit easier to explain. Ancestors lived centuries ago, and they're a close genetic match for the trolls (or so it is said). Each troll believes that they must find out clues about their ancestor (Vriska following Mindfang's footsteps in being a pirate). They also serve as role models, and share the exact same blood color, horn shape, and zodiac symbol as their descendant. Hope this helps.