With another WHOOM, the TARDIS arrives (again) at The Castle of the Two Sisters. As everypony steps out, they see they aren't alone. A tall figure has just finished placing a piece of parchment on the ground. He turns to face them.
"You must be the natives. Funny. Usually intelligent life is humanoid."
"Wait," Rarity says, as she looks to the parchment. "Are you...T?"
Laughing, he nods his head. "My name is Thanos. I have no idea who any of you are, but that doesn't matter."
He raises a fist wreathed in a golden gauntlet, containing six gems that don't quite fit: the Elements of Harmony.
"These are what protect your world, I assume? They're of no use to me, but they're clearly powerful. I'm going to enjoy reducing them to atoms and scattering them to the wind. There's nothing you can do to stop me."
At this, Twilight steps forward. "My name is Twilight Sparkle." She takes flight, her horn glowing as she begins channeling magic. Looking down on Thanos, she continues. "Princess of Friendship, and protector of Equestria. I don't care who you are either, because you have no idea who you're dealing with. If we all work together, with the friendships we've made, there's nothing we can't handle."
"Is that so?" He pulls out a double-edged sword and moves to a battle stance. "Give me your best shot."
Hints are available here.