4-panel episode "Player 5" of webcomic Horned Warrior Friends:

Panel 1 of 4: The Horned Warrior Friends are ready for a roller derby, but Unicorn says "Wait! We need 5 for a full team"

Panel 2 of 4: A voice from somewhere says ""I'm here"" Unicorn says "Who said that"

Panel 3 of 4: The voice says "I've been here all along" Slowly, Horned Chameleon appears from camouflage at their feet

Panel 4 of 4: Zoomed in on Chameleon wearing roller derby gear, big text says "PLAYER 5 HAS ENTERED THE GAME"