Perry decided to go as Ariel, from The Little Mermaid, but took it a step father than one usually would with an Ariel costume. She donned a full mermaid tale, a purple shell bra and rigid, red plastic wig -- meant to imitate Ariel's cartoonish crimson locks -- for a final ensemble that truly made her look like a living cartoon character.
The outfit stole the spotlight at the top of Sunday's big show -- if only for the fact that it's such an difficult costume that Perry needed to be wheeled out on a hand cart dolly because walking was totally impossible.
Then, once fellow judges Luke Bryan and Lionel Richie finally successfully got her to her seat at the judges' table, Perry still took a bit of a tumble.
ET's Matt Cohen spoke with Perry on the red carpet after the show, where she was again brought out on a dolly and admitted that the costume is also restrictive in more ways that just walking.
"This tail is a little bit heavy, and I have had to use the restroom for a while," Perry admitted, jokingly adding, "But I might opt for the wetsuit approach."
"She has no idea I'm in this, and she just started watching The Little Mermaid," Perry shared. "I have started her on the Disney classics, like even the old, old stuff, like Snow White, and then The Little Mermaid, and she really likes them. We've watched all of those."
After Sunday's show, Perry also took to Instagram to share a slideshow of pics and videos giving fans a behind-the-scenes look at the process of getting her into costume -- and she also gave fans a look at her precious pup, Nugget, decked out like Ariel's trusty pal, Flounder.