Well, that all depends on the DM, doesn't it? Theory and practice *can* merge together if that is what the DM decides to focus on, or make more commonplace based upon what kinds of encounters they offer up.
Obviously if a party doesn't have wizards, or doesn't have spells that assist movement, or doesn't have magic items that allow for different types of movement, the DM hopefully learns to recognize this hole in the party's capability and doesn't create encounters intended to exploit it. Unless of course they exploit it prior to large battles in smaller scnearos such that they are informing the party that they *have* this big hole in their capabilities and that they may want to find ways to fill it.
At the end of the day its really part of the DMs job to know what their players and PCs can do, and make encounters to challenge them but not intentionally screw them (unless of course your table is very much that style of 'DM vs players' wargamey-esque table that desires that kind of conflict and resolution-- which is a perfectly fine way to play assuming both sides know that's how they're playing.) And what we had here was a really good lesson that a DM and players learned... unfortunately it just occurred at not the best time. But going forward, it will only make their table stronger and better prepared for games in the future.
The PCs in my campaign come upon things they can’t do all the time. It’s not DM vs Player, it’s characters vs the world.
Just because the come across an ancient unplundered tomb doesn’t necessarily mean they have the means to plunder it. They might not even be able to get in. If they want to, they figure out a way to do it. Maybe they visit a sage, hire a wizard, hire a rogue, wait until they are higher level, whatever.
The PCs explore their world any way they want to. It’s not my job to tell them where they can and can’t go. And the world is the world. I design it, in part, but it’s not designed to make it easy for this group of PCs. It’s designed with history, both written and that of 30 years of other PCs exploring it. It’s a mix of published, homebrew, and random. Challenges are meant to be overcome. But it would be boring if every encounter were custom designed for this group of PCs and their strengths. Overcoming challenges is often about overcoming your weaknesses.
My encounters aren’t created to exploit game mechanics, class features, or whatever. They are designed to make sense in the context of the world and who created the challenge. If the lord of an ancient land wanted a trap-ridden tomb to prevent others from robbing it, then it will be as deadly as it can be. If they could afford mechanical traps, magic traps, constructs, undead, etc, then yes. Poison - that is real poison that kills you if you don’t save, of course. And you should expect it (as my players do) and they don’t go trying to rob such a tomb unless they are really greedy or really need to. And they do it with lots of preparation and creativity.
The intent is not to screw them. But they have to be smart and pick their battles, and plan and prepare for the tough ones.
Like the first tomb in Raiders of the Lost Ark. it was clear that the unprepared died quick deaths. Indy was prepared, and a bit lucky. But the traps weren’t made easier for him. He was just better at identifying the traps and avoiding them.
So I guess I do know what my players and their PCs can and can’t do, and they deal with it accordingly. The encounters challenge them, with the understanding that not everything, or every combat, is winnable and that they may need to retreat, regroup, and come back.
In the OP I think he would have been better off not altering the encounter, and based on the initial description, I probably would have had the monster flee when it took too much damage. And they probably would have learned that they needed to do better about having some ranged weapon options, as well as alternative movement options, and maybe find a way to corner it in more advantageous terrain. But that will depend on their players and whether they would complain that he didn’t design it well for them. On the other hand they would already be well aware that their lack of ranged weapons was a hindrance.
Of course, I’m not big on the BBEG and the “final combat scene” thing so I’m biased. But I generally don’t design encounters for the villain to stand his ground and fight for the death. It’s up to the PCs to do that, and when they do, they always manage it in a manner I don’t expect. There are some obvious exceptions, when the purpose is to destroy a given monster, like an evil dragon. But even that is really, really hard to do without it getting away.
