Harmonic Vengeance

A cheerful voice appeared without warning in Loki's mind. "Hello there!"

Loki grit his teeth. Mentally. "It is generally considered rude to manifest in another's mindscape without invitation."

"Ah, yes, rules of basic decency. So boring. You should be glad I didn't completely overwrite you to be the exact opposite of yourself!"

A little more wary. "...you can do that?"

"Oh, please." The voice sounded as if it were waving its hand flippantly, which it wasn't, because it was a disembodied voice. "I can do anything."

"And what," Loki asked even more warily, "do you want with me?"

"Well, you see, it suddenly occurred to me that both of us are facing a team of six who could be our undoing, and so I thought, why not swap?"

"...Swap."

"Swap! I'll replace the minds of your 'Avengers' with the minds of my 'Elements of Harmony'. They'll be too confused wandering around in their new bodies and abilities to be able to stop us." The voice chuckled. "Better yet, they won't know that the entire team has been replaced. They'll be desperately trying to act like their real counterpart, afraid of the conclusions others will jump to in times of crisis like this. It'll be just so much fun!"

"If you can really do anything, like you say, then why can't you just vanish both pairs out of existence--or turn them into opposites of themselves." His mental voice dripped with sarcasm.

"Oh, I could. Easily." A bored tone that sounded as if the voice's owner was examining his fingernails. "But really, this will be just so much more entertaining!"

"Hmph. I suppose so. And what if I refuse your offer?"

"Hmm?" Hysterical laughter. "Oh, that's adorable! You actually think that I need your consent for this!"

And on that disconcerting note, Loki was alone in his mind again.