"Mwahahaha!" the human twirled his mustache. "You can't hurt me, Twilight. I am immune to magic! Now bow down to your new master!"
Twilight tilted her head and curiously activated her horn to magically examine the new arrival. Strangely, his claim seemed to be more or less correct. Sensing no feedback of any kind whatsoever from her magical poking and prodding, he did seem to have some sort of anti-magic bubble around him. Still, having encountered anti-magic several times in canon already, she had very little reason to be surprised by it now. In this case, the effect didn't appear to be centered around any particular part of his body, and he wore no visible jewelry. So probably not a charm made of material similar to Chrysalis' throne. And while magic couldn't seem to penetrate the barrier, she didn't feel any particular draining effect, so he wasn't eating it, like Tirek did. If anything, this effect most seemed to resemble what The Smooze did.
"Neat!" Twilight giggled, conjuring up a sphere of perfectly ordinary stone around his entire body, just a couple feet beyond the range of his anti-magic sphere.
It took nearly ten minutes for his air to run out, but once the banging from the inside stopped, she teleported the stone away, and began dragging the unconscious human by her teeth back to her lab so that proper science could commence.