Excellinor is a witch and she is the mother of Alvin the Treacherous.
Alvin brought Hiccup to the prison and locked him. Hiccup met Excellinor and she tells hiccup about the story of Grimbeard the Ghastly. Hiccup escaped the cell to go away from her. Later, Alvin met Excellinor at the rope bridge, but there is fire below. The rope bridge snapped and they both fell to the fire.
In Flashburn's School of Sword fighting, Excellinor mentioned that the founder of the king's lost things will be the next king. Hiccup has the king's lost things, except the crown and the jewel. Excellinor told Hiccup to get the crown. When Hiccup founded the crown, she poisoned him with vorpent venom, but he is immune to it. During the sword fighting competition, Hiccup won, but Excellinor told Snotlout to throw a stone at Hiccup's helmet to reveal a slavemark on his forehead, which means he is a slave. The king's things are with Alvin.
In Amber Slavelands, she uses slaves to find the Dragon Jewel. Hiccup disguised as one of the slaves and he founded the jewel when he was brought down by the sand-dwelling dragon. Alvin took the jewel.
When Snotlout captured Hiccup, Excellinor congratulated him. Later, when Hiccup got the king's things, Snotlout came to him and repented. he disguised himself as Hiccup and he got shot by Excellinor instead of Hiccup.
When Hiccup went to the island named Tomorrow, He got crowned as king instead of Alvin. Hiccup's Dragon Jewel turned out to be fake. When Hiccup met Furious, Furious mentioned that the real jewel is in the lobster claw necklace. furious repented. When Excellinor is about to stab Hiccup, Furious blocked her and he got stabbed instead of Hiccup and he threw her to Woden's Blowhole and died.