"You have to be your own worst critic," singer-songwriter Joss Stone told her mentees, Anilee List and Grace Kinstler.
Stone jumped at the opportunity to mentor these young singers and said that it's important for her to pay it forward to the next generation.
"Music is gorgeous, our way of communicating with each other, " Stone said. "Sounds -- aren't they wonderful? It brings so much joy to everyone [and] when we're doing our duets, we're bringing joy to each other."
Stone is just one of the celebrities who have been recruited to help the "Idol" hopefuls find their way. Singer-songwriter Ben Rector is singing with contestants Wyatt Pike and Graham DeFranco and said he was surprised by how the experience made him feel.
"I didn't anticipate how much I would like them and want to hang out," Rector said. "I'm too invested now. I feel like a proud older brother."
Grammy-nominated artist Brian McKnight will sing duets alongside Alana Sherman and Andrea Valles.
McKnight offered his mentees one clear piece of advice: "From a performing standpoint, you have to know who you are. If you can go out on stage and be that, you'll always win."
Jimmie Allen will return to the "Idol" stage, this time as an all-star. The country star previously auditioned for the show and made it to Hollywood Week in 2011.
"It's cool to be back," Allen said. "These contestants got farther than I did."
Allen is mentoring Alanis Sophia and Cecil Ray, but went beyond the scope of their on-stage performances with his advice.
"I said, 'Listen, you're a singer right now but you're at the point where you need to transition to an artist,'" Allen told the contestants, stressing that they need to have a plan to grow after the show ends.
"American Idol" airs Sunday and Monday at 8 p.m. ET/PT | 7 p.m. CT on ABC.