Last week, the Mashup Mondays post-season kicked off with Patrick Stump's rockin' cover of Big Boi's "Shutterbug," and this week we've got another special Fall Mashup for you. Who better for a Mashup Monday than the YouTube cover specialists Karmin? The couple came to Billboard's studios packing not one but two mashups: Foster The People's chilling summer chill-out "Pumped Up Kicks" and Nicki Minaj's booming "Super Bass." Watch them both in the player above.

Photos: Karmin's Mashup Behind-The-Scenes

Karmin at Billboard

"Covering Foster The People's 'Pumped Up Kicks" was definitely a departure from our YouTube raps and hip-hop stuff," Karmin's Amy Heidemann says of putting the duo's voice-and-keys spin on the mellow, menacing rock of "Kicks." "It's just different. That's the kind of music that we listen to."

"We decided to change up 'Super Bass' today just because it's one of the favorites, maybe because we had Questlove in the original [cover they made]," Heidemann said of their piano-infused take on Minaj's summer hit. "How do we make it better? Not possible. So we tried to break it down a little."

Listen To "Crash Your Party"

"Something that we're super comfortable with is covering songs, just the two of us" she says of her work with partner Nick Noonan. But that's not all; they also turn that idea on it's head. New single "Crash Your Party," a preview of a new album due next year, was released on iTunes not only with full vocals but also as an instrumental, "so you can cover it!" they announced excitedly on their website.

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MORE VIDEO FROM KARMIN'S BILLBOARD VISIT:

Karmin does a special take on Nicki Minaj's "Super Bass."