Charmcaster is Hex's niece. Like Hex, she uses magic, but instead of using a staff, she wields a bag from which she can draw all manner of items, such as magical explosives, throwing blades, or even various clay animals to enlarge and animate. Although small, the bag seems to have something of a pocket dimension inside (basically a magic satchel), allowing Charmcaster to store things within it that logically should not fit (at one point, she produces Hex's magic staff, an item that is at least four feet tall). The bag also found its way back to Charmcaster under its own power. She is also skilled in various magical spells, although it's clear that because of her inexperience, she isn't as powerful as her uncle. Although she (like many other villains) dislikes Ben, Charmcaster especially despises Gwen on account of their shared affinity for magic, similar to Ben and Kevin's rivalry.
In her debut appearance, "Tough Luck", she busts her uncle out of prison and assists him in trying to steal the Keystone of Bezel. She manages to trick Gwen by putting on an act about hating her uncle, only to swipe the Keystone while hugging Gwen. She then gives Hex the Keystone. In the end it's revealed that Hex needs the Keystone to recreate the Charms of Bezel, and that she is manipulating her uncle into doing it so that she can take their power for herself. In the end, her powers, like Hex's, seem to be absorbed by the Keystone.
Charmcaster returns in "A Change of Face", her powers having regenerated since her recent encounter with the Tennysons. She attempts a body swap spell with Ben, hoping to take advantage of the Omnitrix in order to boost her magic. Her efforts fail, however, as her three attempts end in swapping with Gwen, being returned to her normal body while Ben and Gwen are swapped, and returning Ben and Gwen to their normal bodies respectively. She is arrested at the end of the episode, and her bag is tossed into the sea. She is last seen in a juvenile detention ward, where she is about to be beaten up by two female inmates whom Gwen spurned while she was in Charmcaster's body. Gwen procures her spellbook during this period, and keeps the item as a souvenir, eventually learning to use it.
Charmcaster makes a small cameo at the end of "Don't Drink the Water", where she is seen taunting her uncle (who has been reduced to an infant by the Fountain of Youth) and saying that she's giving the orders now.
She appears in "Ben 10 vs. The Negative 10" as part of the Negative 10. Although loyal to Driscoll and his plans, she is more concerned with crushing her arch-rival Gwen than anything else. She also is shown to have a slight rivalry with fellow teammate Rojo.