I really liked the idea about combining timelines. I also had nothing happen after the boss, but assumed that was the current end. Took a while to realize, but I liked the fact that the fireball only works after the calamity which shows a bit of lore and mystery as to how the fireball was actually learned! (Maybe its a bug, but I like to think of it as a sneak-peek).
Bugs:
The corpses still pivot to the player
The trees are not YSorting with the player
The tilemap sometimes shifts while moving, revealing gaps between tiles