You can make your own OCs, use characters, but please know this is AFTER Dragons rising (DR) part 2, so Jay hates Nya for winning the tournament, Kai is NOT stuck in the nether-space (not anymore) and some characters like PIXAL, Darreth, Misako, Wu, Garmadon, Skylor (ect) are probably dead! But hey, I'm not caging you do what you want-

Go on! Leash your creativity!