Lanefan
Victoria Rules
My answer: whatever lengths makes sense for that creature.Every DM has their own perspective on this question: do you play the monsters to win?
The thread about how often a PC death "should occur" has had myself thinking on this for a while now. I know, as DM, I can throw whatever I want at the PCs, and while I don't think success should be guaranteed to the players, I do feel the point is generally to make certain they have a fighting chance--perhaps even a fair one on occasion.
But how cunning and resourceful should their opponents be? What lengths should they be willing to go to defeat the characters? (dependent on their personality, alignment, behavior, morals, etc. of course)
Mindless zombies aren't going to do anything tactical or strategic. They're nothing more than self-propelled punching bags or target practice unless the PCs are abysmally stupid.
The stereotypical Evil Wizard, on the other hand, is going to do whatever's in his power to deal with the threat posed by the PCs, once he becomes aware of it. Note however that "deal with the threat" can take many forms, from outright killing to capture to charm to diversion to etc. For example, to temper their threat against him he might have an agent recruit the PCs to deal with some other adventure instead, in hopes that other adventure does them in while leaving him an avenue of plausible deniability.
Situationally dependent. If they've been cautious and-or done some scouting and info gathering, foreshadow away and give them ample warning; but if they just face-charge in without a second thought then they're yours to kill as you please.How much foreshadowing should the DM feel necessary to warn the players, "Hey, this is going to be a tough fight, perhaps a TPK, so I'm giving you hints of a warning here..."?

Tough. That's what you get for taking on powerful people (and, mechanically, is part of why those powerful people are worth so many xp and-or carry such a high CR).While "not fun" for the player in question, one tactic is using magic or terrain to isolate one PC from the party; either to deal with that character or remove them from the battle while the other PCs are dealt with. This typically greatly increases the monster's chances of defeating the party (the "win").
Another strategy is using a familiar or similar creature or magic to spy on the PCs to observe their strategies, strengths, and weaknesses. This allows your monster to gauge which PC is the greatest threat and in what fashion, so they can counter the PCs as well as possible.
When the adversaries are multiple casters, such as a Hag Coven, this creates situtations which some players might feel are "unfair" and certainly "un-fun".
The way I see it, if the PCs can do it then - given the right circumstances/equipment/abilities - so can their foes. A Hill Giant isn't going to use a crystal ball to scry on anyone but a spellcasting Vampire sure could - if she had one. If the foes are known to have any Druids (Nature Clerics) among them then the players know any animal or bird is to be treated with suspicion because their own PC Druid uses shapeshift for spying and scouting all the time. If the foes have long-range Clairvoyance and can target a PC then why not do it?
Note that the same restrictions apply to the foes, of course, as to the PCs: for example if the foe has never seen any of the PCs then any scrying the foe has can't be used on them.
That's where having an NPC adventurer in the party can be a real help: the NPC bailing out is a pretty good clue that the PCs should probably follow suit.For myself as a player, since I often DM, this has never been an issue for me. And while I feel a primary goal of the game obviously is for everyone to have fun, I sometimes find myself at odds because what is fun for myself as DM is a believable world which challenges the PCs, not a game where the players just get to enjoy themselves and "win" all the time.
The last thing I enjoy and very rarely ever do is bail the players out of the situation. I try to give them warning, the chance to learn what they can instead of just charging blindly ahead, retreat (to a point---sometimes you are just in too deep!) and regroup, etc. but if they fail to take advantage or think of such things for themselves, I often feel like they have no one to blame but themselves.

I've got a similar one coming up soon (i.e. we ended last session on the cliffhanger leading into this encounter) - I-as-DM know that between their items and abilities they've got the means to potentially deal with it with only low-to-moderate risk but if they don't think to use said means and instead try something else they're probably hosed before they start.I know the battle looming ahead for my party looks bleak for them from my point of view. While well-equipped and working well as a team, I see the potential for a TPK, particularly if I separate the PCs from one another and deal with them as smaller units instead of a whole group.
That's the thing: parties - as opposed to individual characters - can be surprisingly resilient things provided they're willing to use their exit strategies and getaway cars.Weeks ago, I posted about the dragon encounter the PCs faced. Even though only 7th level at the time, the managed to "fend off" an Adult Black Dragon (CR 14), at the loss of a party member. Through some luck and planning, they managed to avoid the second encounter as the dragon hunted for them after resting. So, perhaps this encounter will go better for the players than I am imagining. We'll see.