so are we supposed to be able to read minds to play this game? because how should someone know how to do it like that without game over like 20 times.
well the game does try to teach through gameplay that enemies may need to be made vulnerable to attack. it is also learned that the sword is the primary method of dealing damage and all prior enemies have been disposable by using the sword. as such, it stands to reason that one would use their sword to attack and destroy the boss.
if one tries to attack him prior to his armour being broken, they would notice that their sword doesn't work, and it gives a generic clanging sound to indicate that the hit has been defended one way or another. when the tail cue is given and it is understood to swing on it, one notices that the roof drops onto the enemy and his skin chips. this is a cue indicating to break the armour in order to make the enemy vulnerable, and when the armour is completely broken, the design of the boss also changes to reinforce vulnerability.
i think the game is giving pretty reasonable design context and information to tell what to do.
