On the final night of Battles, mentors Halsey, CeeLo Green, Thomas Rhett and Keith Urban help Coaches Kelly Clarkson, Jennifer Hudson, Adam Levine and Blake Shelton prepare their artists to go head-to-head in dueling duets.

The coaches enlist iconic superstar Mariah Carey to act as Key Advisor on the second night of Knockouts, when the coaches pair their artists to perform solo, then select just one of them to move on to the Playoffs.