Here is the voice cast of characters who are not members of the Guardians of Peace and Harmony, but appear to join in every now and then. Please note that this too is subject to change for a variety of reasons.

Kelly Sheridan as Starlight Glimmer
Corey Feldman as Slash
Peter Lurie as Leatherhead
A. J. Buckley as Pigeon Pete
Robbie Rist as Mondo Gecko
Tom Kenny as Dr. Tyler Rockwell
Zelda Williams ad Mona Lisa
J.B. Smoove as Bebop
Fred Tatasciore as Rocksteady
Nolan North as Bishop
Fred Tatasciore as Lion
Craig Blair as Tracey Sketchit
Veronica Taylor as May
Amy Birnbaum as Max
Emily Bauer as Dawn
Eileen Stevens as Iris
Jason Griffith as Cilan
Haven Burton-Paschall as Serena
Michael Liscio Jr. as Clemont
Alyson Leigh Rosenfeld as Bonnie
Rosie Reyes as Lana
Marc Swint as Kiawe
Laurie Hymes as Lillie
Caroline Spinola as Sophocles
Rebecca Soler as Mallow
Eddy Lee as Gladion
Rob Morrison as Rotom Pokédex
Zeno Robinson as Goh
Cherami Leigh as Chloe Cerise
Alejandra Reynoso as Liko
Anjali Kunapaneni as Roy
Olivia Vidas as Nemona
Henry Mason as Arven
Cat Protano as Penny