Season 4/7 Something shows up at the island somewhat unexpected (meteor and iceberg) that holds someone that we dont know (visitor and fire king) about until about week seven when they escape then at the end of the season they do stuff that will alter the map next season.

Season 5/8 The map gets altered in a corner of the map (Paradise/Jungle) due to the person from before later in the season something shows up on the map that stores energy and starts moving around at the end of the season the thing ends at loot lake (kevin/weird floating runes)

Season 6/9 first nice, second tbh this one stumped me, the only similarity that i could think of is how at the end or endish of the season an explosion happens at Loot Lake. If u guys can think of anything else plz reply in the comments