Anything I spring on the PCs is something that functions within the rules, even if I have to pull out stuff like Incantations to provide a means by which the low-level NPC summoned up some critters that were way past his pay grade.
I've been in *far* too many games where the NPC used something and then the PCs were like, 'that's pretty cool and effective, I try to use that' and get the 'it doesn't work for PCs' excuse. That's just sloppy, IMO.
Games have rules for a reason, to create a sense of fairness and challenge, and it's not like I can't do any darn thing I want by just having the bad-guy have a unique spell or custom feat or freaky magical mutation as a result of huffing too many potions in his dad's alchemy lab as a child. But *I'll* know how it happened, and if I don't want the players to get access to it, I'll show them the downsides (yeah, he can do X, but the side-effect is that he's got a point-buy of 10 and is completely insane, or yeah, he used an Incantation, and it only requires that you be a blood-descendent of the demon whose minions he summoned).
If I were to ignore the rules in designing my encounters, the players victories become meaningless. They aren't playing the game, they are just suffering through whatever rambling story I wish to tell them, with no reward for mastery, no use in engaging in any sort of strategy, no value in taking any knowledge skills (since I'm just making crap up), no sense of fairness and no 'game,' just me and my captive audience. I've been that captive audience, stuck with a bunch of loot that doesn't work for me (just like the thrice-cursed Drow magic items of 1st and 2nd edition, which were removed from the game for a reason), having just fought spellcasters with magical spells and abilities that I'm not allowed to have. What's the point of even calling it D&D if the stuff the DM is throwing at me has nothing to do with the rules of the game?
I've been in *far* too many games where the NPC used something and then the PCs were like, 'that's pretty cool and effective, I try to use that' and get the 'it doesn't work for PCs' excuse. That's just sloppy, IMO.
Games have rules for a reason, to create a sense of fairness and challenge, and it's not like I can't do any darn thing I want by just having the bad-guy have a unique spell or custom feat or freaky magical mutation as a result of huffing too many potions in his dad's alchemy lab as a child. But *I'll* know how it happened, and if I don't want the players to get access to it, I'll show them the downsides (yeah, he can do X, but the side-effect is that he's got a point-buy of 10 and is completely insane, or yeah, he used an Incantation, and it only requires that you be a blood-descendent of the demon whose minions he summoned).
If I were to ignore the rules in designing my encounters, the players victories become meaningless. They aren't playing the game, they are just suffering through whatever rambling story I wish to tell them, with no reward for mastery, no use in engaging in any sort of strategy, no value in taking any knowledge skills (since I'm just making crap up), no sense of fairness and no 'game,' just me and my captive audience. I've been that captive audience, stuck with a bunch of loot that doesn't work for me (just like the thrice-cursed Drow magic items of 1st and 2nd edition, which were removed from the game for a reason), having just fought spellcasters with magical spells and abilities that I'm not allowed to have. What's the point of even calling it D&D if the stuff the DM is throwing at me has nothing to do with the rules of the game?