Watch Shawn Mendes Sing Fall-Themed Tweets on 'Tonight Show'

Andrew Lipovsky/NBC
Shawn Mendes performs on The Tonight Show Starring Jimmy Fallon on Sept. 22, 2016. 

Shawn Mendes did double-duty on The Tonight Show on Thursday (Sept. 22), performing his single "Mercy" as well as sitting in with the Roots to participate in the weekly Hashtags bit. With host Jimmy Fallon reading off the names of the submitters for this week's theme (#FallSongs), Mendes joyfully sang the original lines set to the tune of his hit "Stitches," as well as smashes by other stars.

Watch Shawn Mendes Beg for 'Mercy' in New Music Video

"Watch me sneeze until I can't breathe/ Allergies are gonna kill me," he sang to the tune of his own "Stiches." After gently, but repeatedly reminding the host that he's "much older," Mendes tried a lyric about Starbucks' pumpkin spice latte to the tune of Simon & Garfunkel's "The Sound of Silence," then tried out a track about leaves (to Coldplay's "Yellow"), one about Halloween (to Naughty By Nature's "O.P.P.") and yet another about leaves (to Adele's "Hello"). 

Check it out:

And here's Mendes singing "Mercy":