Bizarre Seasons: Eliéra’s seasons aren’t actually all that bizarre, but they are more complicated than the standard model. It has something resembling our earthly seasons (based on the binary system it occupies, rather than non-applicable axial tilt: it is summer when the planet is between the stars, increasing insolation, and winter when it is on the far side of the primary from the secondary – pure solar effects magnified by chaotic atmohydrospheric effects), but overlaid on this is the “deep seasonal cycle”, caused by the 2,856-year orbit of Súnáris around Lumenna. When it’s at periapsis, in deep summer, summers are hot and winters mild; when at apoapsis, in deep winter, summers are cooler and winters cold.
Kythera (Thirteen Colonies) has a similar deep seasonal cycle, but its is caused by an oscillation in oxygen levels and planetary albedo that leads to warming along with growing oxygen levels punctuated by planetary wildfires that deplete oxygen again and whose shifts the albedo enough to plunge the planet into winter. And repeat.