"Mwahaha" the human twirled his mustache. "Not only am I immune to magic, but so is my clothing because it's from a universe without magic too! And even if it wasn't, my physics bubble extends at least half a foot or so beyond the range of my clothing, so I am totally immune!"
"Oh no! How horrible!" Rarity gasped in terror at the prospect of succumbing to such a tastelessly dressed villain.
"Please don't eat me," she begged. "I've hardly any muscle on me at all, so I'd probably taste...well, to be fair I'd probably taste marvelously, because I'm Rarity and everything about me is marvelous. But please dear, at least think of your figure. All this delicious pony meat would go straight to your thighs, and you wouldn't want that now, hmm?"
"What?" the human recoiled. "I'm not going to eat you. Human don't eat horses. Except the French I think, but nobody cares about them anyway."
Donning her spectacles, Rarity stopped her cowering long enough to examine the human's mouth. Sure enough, his teeth didn't seem particularly well suited to rending flesh from bone, and were desperately in need of a good whitening cleanse. But she'd have to take that up with him later.
"Well in that case, please don't ponynap me and chain me up in an underground slave mine!" she begged. "Because I've already done that, and it simply wouldn't do for a lady of my caliber to have the same tragedy befall her twice. Whatever cruel fate you have in store for me, please let's try to be original, darling."
"Wait, are you actually giving up?" the human pondered the novelty of the situation, still twirling his mustache. "Huh. So, I'm just going to be honest here. This is the first time I've made it this far, and I'm not really sure what to do now."
Her eyes narrowed.
"Surely you don't mean to tell me," Rarity's voice took on an icy tone, "that you came all the way from another universe to be villanous and you couldn't even be bothered to think up a plan?"
"Uhh, no?" the human replied nervously, taking a step back from the very annoyed pony now walking towards him. "I figured magic immunity was overpowered enough that I could wing it."
"I'm sorry," she whispered softly, her eyes half lidded over. "Did you say, 'wing it?'"
"...yes?"
"What kind of blundering, amateurish, second-rate villain are you?" she demanded. "I am Rarity, and I expect to be accosted by only the best villains!"
"But wait! I can-"
Before he could finish his sentence, a roll of bright red ribbon bathed in a magical glow unfurled itself from a roll and wrapped itself around his ankles, his wrists, his neck...his whole body, really. She then lifted him by that same ribbon and hung him upside down from the rafters to think very carefully about the error of his tacky ways.
No need to operate your magic inside the anti-magic bubble when you only need to pull on the ends of a rope to pull a knot tight.
"Hmph!"