You've Ben Charmed

AU involving the ‘A Change of Face’ episode of Ben 10. Gwen fell just short of the spell bubble, and so Charmcaster was victorious in her switching with Ben’s body.

However, initially boastful about her victory, Charmcaster found that she couldn’t get the Omnitrix to work properly. As it turned out, counter-measures installed in the device caused the AI to notice that something was very WRONG about Ben. After having been with him for so long, it was accustomed to his brain waves and thoughts. As such, in a bit of confusion from the AI, it went into a locked mode. After all, a genius of Azmuth’s caliber would have likely foreseen possibilities like this.

As Ben and Charmcaster struggled and messed around with the Omnitrix, they accidentally managed to activate the device’s recalibration mode, and in effect caused the AI to reach out with its scanners and sense Ben’s mental signatures within Charmcaster’s body. Acting upon this, the watch quickly hopped over to Charm-Ben, and in the process changed its physical appearance.

This left Charmcaster, in Ben’s body, without the Omnitrix AND any access to magic due to a lack of magical aura in Ben’s body. This also left Ben in Charmcaster’s body, and though Charmcaster’s body possessed a spectacular magical aura, Ben understood next to nothing about magic at all. Needless to say, neither of the two were liking their situation. 

Changing back would prove to be a bit difficult, as even though Gwen knew magic, she wasn’t as experienced as Charmcaster with it, and attempts at making another bodyswap spell resulted in set backs due to Gwen both lacking the control and experience necessary AND fudging up just enough in making the potion due to wanting Charmcaster gone AND feeling some jealousy over Ben now having access to potential magic. It didn’t help that certain shops were also oddly out of a proper stock of needed ingredients. 

Charmcaster, annoyed with both of the cousins as a whole and their inexperience, along with Ben’s disparaging comments about magic while in her former body, decided that the best course of action would be to try and teach them about the finer details of magic and how it PROPERLY worked. Perhaps after doing so, at least ONE of them would be able to actually have the skill to put together and use the bodyswap spell without a hitch. Preferably she would rather her former body manage to do so, instead of having to rely on the ‘novice’ and bruise her ego.

… but there was only one minor hitch in this plan. Trying to teach Ben magic was like trying to smash a brick wall with a wet sponge. It shouldn’t take that long to finally get it all to stick, right?