the "eyes" in level 4 don't help your clue. the whole time i was thinking, why is he calling this level shape a zol, does he not know what a zol is? would be a lot clearer if your level 4 shape didn't have eyes as well.
also, the level 4 boss room door locks behind you, forcing the player to exit the game if they don't have the whistle yet.
edit: through level 5. i enjoyed it a lot more than 4. the charging darknuts are the best new enemy i've seen in the contest so far.