Sage

The Skrullbrid was a Skrull genetically combined with a Witch, a Werewolf, a Vampire and a Fairy until they were "unmerged" from the four species stated above. Being a Skrull, changing gender for them is just like changing hair color. The Skrullbrid is gender fluid, hence the pronoun "they" is used for them.

Becoming the Skrullbrid
Prior to February 4, 2016, Charmcaster and the Skwitches planned to create the most powerful weapon in the universe. They decided to steal Dan's powers, and merge the DNA of a Witch, Vampire, Fairy and Werewolf with a Skrull. Since witches are nature's servant and vampires are nature's abomination, witches who become vampires will lose their magic. However, the Skwitches managed to cast a curse on Cass Rayne, a witch, reversing her ability to generate magic as it became the ability to absorb magic. Charmcaster and the Skwitches flew to Mykdl'dy as there is a machine that would allow them to create the "weapon" on that planet and managed to beat Ice Prime and the others to it.

They waited for the arrival of Ice Prime and the others and followed behind them. Because the temple on Mykdl'dy was sealed by a Jensen witch, it could only be opened by another Jensen witch. Billie wanted to quickly destroy the machine, but the Skwitches managed to hold them off and the merge was successful. Sage became the Skrullbrid. Billie and the others tried fighting against the Skrullbrid but were too weak. They decided to flee the temple. Billie cast a spell to seal the temple. Sage, having only the powers of a Rayne witch and a Summers witch, was unable to break the spell initially. The Skwitches and Sage stayed trapped in the temple for a few days before they somehow eventually got out.

Sealing off the Magic School
When they returned, the Skwitches managed to transfer the powers of a dead Jensen witch (who was lying in the spiritual plane instead of the Jensen Ancestral Plane for some reason). After they freed Ahura from the Skwitches' compulsion, the Skwitches got the Skrullbrid to attack them. The Skrullbrid tried to attack them, but the magic school's protection didn't allow the Skrullbrid's powers to enter. Hence, they decided to surround the magic school in an impenetrable force field that didn't let anything out and left all of them to starve to death in the school. Ahura managed to get out, but the Skrullbrid defeated Ahura and bit him before opening up a hole and throwing him back into the school with no way out.

Together with Zack
Nevertheless, they managed to break out of the force field with Ahura's help. They found out that by using the Jensen's specialty spell, the Skrullbrid managed to bind the force field to the Jensen bloodline, the Summers bloodline and the Rayne bloodline. They need a Jensen, Summers and Rayne witch to break the force field. In addition, they also need to negate the rage energy bound to the force field and a fairy was needed as well. The force field didn't allow anything to get out of it, not even portals can be opened to another location outside the force field or another plane. The only way to get out of the force field is to die, so that the spirit can travel to the spiritual plane. Hence, Ahura decided to accept his fate and he died. Ahura met Laurelle Rayne in the spiritual plane and using him as an anchor, she channeled the power of her descendants and possessed K'Line, who was linked to her due to the Absolution ritual. Laurelle got Megan Gwynn to help break the force field before temporarily killing Katherine with a spell. Unbeknownst to her, another witch has seemingly possessed Julie and she cast a spell to send Laurelle back to the spiritual plane before returning there herself.

They decided to throw the two Skwitches into the training room, undoing the Absolution ritual they took part in, thus stripping them of Absolution permanently. Debora, J'ann and the Skrullbrid came and demanded that they return K'Line and Julie. Debora and J'ann's powers started to go out of control because with K'Line and Julie's Absolution stripped from them, Debora and J'ann's powers have now been doubled. Zack revealed that he had been there all along and he turned visible and sent the two Skwitches into the training room as well, stripping Absolution from them. With that, nobody channels the spirits any longer. Zack tried to do the same with the Skrullbrid as well, but they managed to grab Zack through the portal and kidnapped him.

They brought Zack to Charmcaster and for the first few days, they tortured Zack until one day, the both of them started chatting and developing feelings for each other. The Skrullbrid, at times, even took on a male human form to please Zack's desires. They bound and gagged Charmcaster and on Zack's birthday, they gave him a toast. Unfortunately for them, Charmcaster broke free and escaped. She decided to seek Ice Prime and the others' help and showed up at Magic School and was reluctantly invited in by Ice Prime. Since the Skrull Spaceship was cloaked and she left her staff there on purpose, she was able to let it release a huge explosion of mana which could be tracked down by Gwen's powers. They arrived at the spaceship, rescued Vinn Nguyen and trapped Sage, the Skrullbrid in an anti-magic force field. Zack was "rescued" from Sage, albeit against his wishes. Unfortunately, during the fight, Charmcaster escaped and rescued the Skwitches from the anti-magic cells they were kept in.

Trapped in the Mirror World, Powerless
Sage was then confronted by Charmcaster and the Skwitches for not being loyal to the Skrull Empire. He was stripped of his powers and made a normal Skrull.

Zack was thrown into an anti-magic cell as they thought that Sage has cast a spell to make him fall in love with them and would try to rescue Sage. Ice Prime, Billie and Sky wanted to vanquish Sage, but Irvin, Silver and Leo believed that Zack and Sage were truly in love. Ice Prime came up with a plan to vanquish Sage, and Irvin, Silver and Leo planned to keep Sage alive. Silver lured Charmcasters and the Skwitches into a Starbucks cafe that had already been spelled by Silver to be free of magic, but they did not know that Sage has already been stripped of their powers and "unmerged" from the four species they were merged with. With Charmcaster and the Skwitches trapped in the anti-magic cafe, Ice Prime and the others decided to save every single Avenger the Skrulls had abducted and he decided to vanquish Sage. However, Silver and Irvin managed to convince Ice Prime to trap Sage in the mirror world, which is a fate worse than death. Zack somehow escaped his prison, and arrived on time just to see Sage entering a glass window. He secretly took that piece of window back to his dorm, where they could see each other everyday.

Powers and Abilities
Sage is a Skrull possess all the abilities native to their species, but they also have a lot of knowledge about magic as they had to learn all about witchcraft since they volunteered to become the Skrullbrid. Prior to being stripped of their powers, Sage also had the abilities of a Vampire, Werewolf and a Fairy, and could siphon magic from any source, including from their vampirism.
 * Skrull Shape-Shifting: Like other Skrulls, Sage can shapeshift. They can mentally cause the unstable molecules that comprise their body to become pliant, enabling them to assume other forms through muscular expansion and contraction. They can assume the form of someone but not their powers. They can easily change their sex by shapeshifting into another form.
 * Elasticity, Plasticity, Elongation: Their shape-shifting abilities allow them to alter their bodies in much the same way as Mr. Fantastic, so that they can stretch to great lengths, or form other shapes with their bodies, such as balls, parachutes, or anything else.
 * Flight: They are able to fly by shape-shifting a pair of wings onto their back, or turning their arms into wings.
 * Size Alteration: They are also capable of altering their size independently of altering their form, allowing them to grow or shrink while maintaining their current form
 * Mimicry: They can mimic sounds and voices when they shapeshift. This is mainly used in conjunction with the shapes they shift into.

Trivia

 * Sage is genderfluid. The pronoun "they" is used for Sage.
 * As such, they frequently switch between female and male forms.