The singer appeared on late night to promote her upcoming album and current gig on "The Voice," but with an entire hour to fill, there was time for a few games, performances and one viral video that took place outside of the studio.
Keep reading for the three can't-miss moments from the show.
"You, without knowing it, was kind of a reason for this," she explained when Fallon asked about her quitting marijuana cold turkey.
"I've always been very stoned on your show. Remember the last time I was here I was dressed as a bunny rabbit, a cat? There's a reason for that: I was high," she added.
"I'm actually the most passionate with what I'm doing with this record … this record for me at this moment is the most important album that I've ever made," she said of her reasoning to stop smoking. "I wanted to make sure I'm super clear about the way I'm talking. I had a dream I would die during my monologue on 'SNL' for some reason, that I'd get so stoned and die. I kept having this nightmare. It's like no one's ever died from weed but no one's ever smoked as much as I did."
In one final fun game, the two sang popular songs that had been translated into Croatian and then back into English using Google Translate.
First, Miley took on Ed Sheeran's "Shape of You," where lyrics like "I'm in love with your body" became "I like that cadaver." When Jimmy tackled "Super Freak," the title lyrics became "she is really weird, yes!"
They brought it home with a duet to "Ain't No Mountain High Enough," which hilariously translated back to "Landforms don't prefer to get high."