Re: Boss Preferences
Funny thing is, I've seen a lot of games that didn't have a clue other than to just let the player fumble around until they figured it out (usually with pattern/puzzle bosses). Sometimes there are clues, sometimes not.
In the case of the "must be killed by boss without hurting him" idea, you could always have some story elements/etc. to clue the player into the idea. They just don't need to be "too" obvious. Maybe have the idea that the boss is known to characters in the game and they mention that no known weapons have any effect on the boss character other than to tick him off...lol. But, there would still need to be "some" mystery as to what the player is supposed to do.
In the case of a destructable environment, perhaps the weapons loadout would be used for that purpose (as a way to block/slow down the boss while you are trying to place the collected items). Then, there would be a purpose for all the weapons, even thou they were not to be used on the boss.
Perhaps the puzzle portion would be placing collected items at 4 locations that would lead to something opening up/platform raising sort of thing. Something to lead the player into that location. Once the player is on the platform, "something" strange starts to happen (lots of glowing, particle effects and cool sounds...lol). While the player is standing there, the boss comes in to destroy the player (in that location). If the player leaves, the platform is destroyed and the player loses. If the player "stays true" (or some other game related sense of honor/etc.) and stands firm, the boss kills the character JUST AS the player activates the thing that kills the boss character.
I dunno, just an idea off the top of my head. More time and thought could iron out any details. :}