Rainbow Swoop, or Purple Waters, is a backgroundPegasus pony with a light bluish-purple coat, dark gray mane, sea green eyes, and a cutie mark of a purple, orange, and yellow-striped rainbow. He is not named on the show, but he is named "Rainbow Swoop" with a trademark symbol and "Purple Waters" in different merchandise.
In Common Ground, Rainbow Swoop makes a cameo appearance cheering in the crowd during the exhibition buckball game during a tournament in Appleloosa. In The Last Problem, he makes a background appearance flying outside future Canterlot, despite not looking visibly older.
2:24, 2:31 - helping Pinkie Pie with her Hearth's Warming Eve pageant costume; 2:51, 3:12 - talking with "Amaranthine"; 5:10 ~ 6:17 - taking part in the pageant; 20:55 - talking with Cherry Berry backstage
0:30 - approaching the Golden Oak Library; 2:21 - inside the library; 8:25 - cheering for Rainbow Dash; 10:02 - looking at Fluttershy; 16:00 ~ 16:17, 17:57, 19:07 ~ 19:22, 20:15 - flying at the Ponyville reservoir (with several duplicates)
4:49 - on the Equestria Games qualification training grounds; 5:51, 5:56, 6:09, 10:45, 10:51, 11:19, 11:52, 12:24, 18:37 - flying with Orange Swirl and Prism Glider (no cutie mark); 10:56 - flying with Prism Glider (no cutie mark); 11:46 - flying solo (no cutie mark); 13:44 - flying with Orange Swirl and "Bon Voyage"; 20:37 - on a qualifying air relay team with Orange Swirl and Rainbowshine; 20:45 ~ 21:08 - watching the award ceremony from the crowd
A translucent mini-figure toy of Rainbow Swoop was released as part of the tenth wave of mystery pack toys and collector cards and named with a trademark symbol. The collector card depicts him with Soarin's design and states that he "loves to fly over rainbows as fast as he can!"
In the Canterlot Nights expansion set of Enterplay's collectible card game, Rainbow Swoop is named "Purple Waters" on his own card #41 C, which gives him the description "Purple's albums such as 'The Fence' have made him legendary in Equestria. Singing evocative lyrics like: '...and when DJ-Pon 3[sic] starts spinning different tunes, I'll see the Dark Mare of the moon.' leaves everypony hoof-stomping for more!" Enterplay's May 13, 2014 Canterlot Nights card list lists card #41 C as "Full Spectrum, Prismatic Pony" instead of "Purple Waters, Prismatic Poet/Musician".
"...and when DJ-Pon 3 starts spinning different tunes, I'll see the Dark Mare of the moon."