My Ninjago Headcanons
Kai got his iconic scar when he was playing with his Katana.
Ever since the "Ice Emperor" incident, as well as utilizing personas in the field, Zane took up LARPing and TTRPGs - and even has a secret friend group that the rest of the team doesn't know about, not even PIXAL. They meet every Wednesday.
Jay crossdresses, but doesn't ever wear skirts or dresses. Kai will occasionally wear a skirt, but never dresses femininely.
Lloyd's the shortest member of the team - his growth having been permanently stunted due to Tomorrows Tea aging him up physically before he ever went through Puberty. He's also unable to grow good facial hair.
Zane still believes in Santa Claus - Dr Julien programmed him to never stop believing.
Karlof, Skylor, PIXAL, Dareth, and Misako get together every few months and grab a drink. Occasionally, other Elemental Masters will join in.
Some time between the events of Crystalized and Dragons Rising, Karlof and Dareth had a rematch. Dareth still lost - but Karlof commended him on his improvement.
Serpentine often frequent coffee shops. Nothing better than a warm beverage for someone who's cold blooded.
Between the events of Seabound and Crystalized, The New Ninja stopped several potential world-ending threats. The only reason we've never heard of these threats is because they were stopped BEFORE causing widespread destruction.
Cole, Zane, Nya, Lloyd, and Jay all see the same therapist. Kai doesn't need therapy. The therapist very much does.