Addwaitya

Adwaita is a Geochelone Aerio that mastered magic thousands of years ago. He's an evil mystic being considered as the most powerful sorcerer in the universe. He was mentioned in Escape from Aggregor and introduced in Where the Magic Happens and is responsible for the death of Spellbinder, Charmcaster's father.

Appearance
Adwaita is a turtle-like creature with pink mana fire-like energy surrounding his head.

In Enemy of My Frenemy, the flames around Adwaita's head have disappeared and his head has turned the same color as the rest of his body.

In Omniverse, his appearance is slightly altered, with his head now being surrounded by a new necklace with long horns. His head is also wider with his nostrils larger. He wears red armbands with yellow cuffs at the top and bottom. He has donned a red belt with yellow cuffs, fitted with a bull skull at the middle. Beneath the skull is a small, red loincloth.

Background
Adwaita got his hands on the Alpha Rune, an exceedingly powerful magical item (which was actually a piece of the Map of Infinity in disguise) and reached the interdimensional world of Ledgerdomain. He got corrupted by the immense magical power the artifact possesses.

The inhabitants of Ledgerdomain, though most of them were very powerful sorcerers and sorceresses, were unable to defeat him, and their leader, Spellbinder, was forced to send his brother, Hex, and his daughter, Charmcaster, to Earth in order to keep them safe. While he did that, Adwaita murdered him and took control of Ledgerdomain. He had also enslaved most of the people of Ledgerdomain to do his bidding.

Ultimate Alien
In Escape from Aggregor, Adwaita was briefly mentioned by Galapagus. Adwaita was first seen in Where the Magic Happens, when Ultimate Aggregor reached Ledgerdomain in order to get his hand on the Alpha Rune. Chasing him, Ben, Kevin and Gwen were forced to ask for Charmcaster's help in order to reach Ledgerdomain. When the group arrived, Adwaita immediately felt their presence and attacked them. Adwaita also used Spellbinder's voice to encourage Charmcaster to fall to her death (though the team stopped Charmcaster from doing so). When they got to Adwaita's citadel, a Pallorfang attacked them and died after falling off the edge of the land. After a feral fight, Adwaita was surprised by an attack from Ultimate Humungousaur, allowing Ultimate Aggregor to knock him out with a sneak attack and escape with the Alpha Rune. Ledgerdomain then started falling apart and Charmcaster, seeing Adwaita weakened, chose to stay behind to fight him and save her people.

In Enemy of My Frenemy, Ben, Gwen, and Kevin, having returned to Ledgerdomain to save Charmcaster, stumble across Adwaita, who is magically bound to a stone formation while his magic is being drained by a nearby crystal. After destroying the crystal, he is magically handcuffed by Gwen and questioned on what had happened to him. Adwaita claims this was done to him by a "usurper," but does not disclose the individual's name. They then decide to bring him with them to reach the "usurper". On their way there, they stopped at a waterfall. With Ben and company distracted, Adwaita used his magic to dissipate Gwen's mana handcuffs and cast a spell on the water, turning it into a giant water monster, while he went to fight the "usurper". The usurper turned out to be Charmcaster, wielding the Alpha Rune. Adwaita attempted to attack her, but was no match against her with the Alpha Rune, and has his soul sucked out of him for her machine. When her spell is later reversed and all the souls of Ledgerdomain are returned to their bodies, Adwaita is revived as well.

In The Ultimate Enemy: Part 2, Adwaita was seen in a flashback.

Omniverse
He has a short appearance talking to Charmcaster in Charmed, I'm Sure. He has been turned into a totem along with Darkstar and is kept in Charmcaster's bag. Charmcaster is listening to his advice in her plans, but is still confident that she is in control of him, although Adwaita managed to manipulate her. His conversation with Charmcaster made Ben, Rook, and the others think she's crazy.

In Charm School, though Adwaita made no on-screen appearance, Charmcaster talks to him in her bag.

In Third Time's a Charm, Adwaita, along with Darkstar, Hex, and Gwen, are freed from Charmcaster's Bag. After begrudgingly congratulating Gwen on her magic, Adwaita teleports away.

Powers and Abilities
Adwaita is shown to be incredibly strong when he has the Alpha Rune, with Charmcaster claiming him to be the most powerful sorcerer in the universe. Capable of doing spells without saying them, he easily defeated Gwen, Charmcaster, and Kevin. He was even capable of fighting Ultimate Humungousaur without being defeated.

Even without the Alpha Rune and most of his own power being drained by Charmcaster, Adwaita was still capable of performing spells of considerable power. However, he was shown to be no match against Charmcaster when she held the Alpha Rune and easily defeated him.

According to Dwayne, Adwaita retains his normal Geochelone Aerio powers, even though he lacks holes on his torso.

Weaknesses
As a Geochelone Aerio, Adwaita has all the standard weaknesses of his species, though he has less of a blind spot due to the position of his head in comparison.

Though the Alpha Rune did grant him great magical power, it made him extremely irrational and violent.

Without the Alpha Rune, his spellcasting is greatly reduced. While he was in his stone-figure form, he was even more helpless and at Charmcaster's mercy, though he was able to manipulate her, albeit in a more subtle fashion, giving her advice that seemed helpful but ultimately lead to her defeat and his escape.

Ben 10: Ultimate Alien

 * Where the Magic Happens (first appearance)
 * Enemy of My Frenemy
 * The Ultimate Enemy: Part 2 (flashback; cameo)

Ben 10: Omniverse

 * Charmed, I'm Sure (first re-appearance; stone form)
 * Third Time's a Charm

Etymology
Adwaita is named after a male Aldabra Giant Tortoise from Alipore Zoological Garden, India, that lived to be 255 years old and is a Sanskrit word "advitya" that means "something which is second to none".

Trivia

 * Adwaita's name is pronounced differently by different characters.
 * Adwaita himself pronounced it add-wait-yah.
 * Galapagus and Charmcaster pronounced it add-way-cha.
 * Adwaita was a revered philosopher and mystic of his species, whom appeared to achieve godhood.
 * According to Dwayne, no one knows that Adwaita became corrupt.
 * Adwaita's appearance and place of residence is reminiscent of the Marvel Comics villain Dormammu, nemesis of Doctor Strange.