However, this wasn't any ordinary gown. Her tulle Lever Couture design featured sculptural sleeves, an asymmetrical bottom half that included excess tulle material cut into thick fringe strips and a thigh-high slit.
From the diaphanous silver fabric to the architectural structure, the piece created the illusion of moving water. The Making the Cut star accessorized her sparkly number with clear heels and diamond-encrusted studs.
And Heidi's dedication to dressing in the Avatar theme also extended to her beauty, as she opted for a sleek wet hairstyle effect, which made her appear as though she had just stepped out of the pool.
She wasn't the only one to dress the part, either. Her husband, Tom Kaulitz, got in on the action by wearing a metallic silver suit with a matching button-down.
Of course, this isn't the first the couple has coordinated their looks for a special occasion. During the model's annual Halloween party, she made jaws drop in a giant worm costume, while Tom dressed up as a fisherman.
"I only have one look, and I'm going to be very claustrophobic in it," she teased a month before during an interview with E! News. "And I think—I don't think, I know, that it will be the best one I've ever done."
At the time, she estimated it would take her 14 hours to transform into her costume. "I can't let my Halloween fans down," she said. "So I've gotta bring it!"
Although Halloween came and went, it's clear that the America's Got Talent judge is dedicated to raising the fashion bar.