Earth's Mightiest Heroes infiltrate A.I.M. to recover stolen technology in this exclusive clip from the season premiere of "Marvel's Avengers: Ultron Revolution." But Black Widow's undercover team discovers a bigger surprise than they expected! And is that the titular robot in a green, glowing tube?

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The new season of "Avengers Assemble." "Marvel's Avengers: Ultron Revolution" debuts this Sunday, March 13 on Disney XD.