One of the things that a GM has to do now and then is to break certain assumptions with regards to Players and their perception on what can or can’t happen in a given game.
This shouldn’t be taken as a malicious statement of intent, however, but sometimes it becomes necessary to slaughter a few sacred cows to really shake things up and hammer home the impression that the Player Characters are the only people that really matter in the setting. All else is perfectly fair game.
But why do this to begin with? Well, few things can really hammer home the idea that they’re playing in your game than when you suddenly take the campaign direction away from the established canon. Canon is awesome in the sense that it allows players to orient themselves. Consequently, the GM can also break canon to give that slight sense of disorientation, leaving the players to suddenly scramble for purchase and find their bearings, well aware that things aren’t going to be the same from this point forward, and that their actions matter even more now.
Of course, such an attempt should be undertaken with a bit of care and an eye towards making it matter. Going about just breaking everything might backfire with making it look like you’re just out on a power trip. After all, just going about and say, petrifying Elminister might seem cool, but if you slaughter Drizz’t and all the other big name NPCs one after the other then it loses its impact.
Breaking setting assumptions is a potent tool best used sparingly. But if used at the right time, and in the right fashion, you can leave a lasting impression where the players realize that the kid gloves are off and it’s time to get serious.