from my experience i'd say players expect that certain monsters behave a certain way, e.g. trolls regenerate, displacer beasts teleport around and a vampire can suck your blood, rather than a bear has 16 strength 60hp and so on and players value consistency, so if a kind of monster had no fire resistance the first time they've encountered it they should not have it next time only because the wizzard destroyed 5 of them with a fireball. some players read published adventures though and get irritated if a game master changes stuff, but those guys can run their own game where everything is straight from the book rather than adapted to the group.

I'm glad I don't play with people like this.

Ive dmed for 15 years, only putting out the hasbro certified stat blocks is a sign of a bad dm imo. The health stat is way off for most creatures, a house cat should not be able to easily kill a grown man. Additionally most creatures have been thinned down for 5e, so giving them some extra spell options or abilities feels better to me. Additionally narrative reasons to change the block makes sense a lot of the time. If theyre fighting trolls that live in a volcano, fire damage might not be the key that fits the lock.

>so if a kind of monster had no fire resistance the first time they've encountered it they should not have it next time only because the wizzard destroyed 5 of them with a fireball Unless you're fighting Borg, of course

You've met a bugbear. Now get ready for BORG BEAR.

A house cat can't can't easily kill a grown man. They have 1d4 hp against a Commoner's 1d8, and 1 damage against a Commoner's 1d4. Granted, that's assuming the Commoner is carrying their default club, but even unarmed the cat would have to be very lucky. Though one in eight Commoners have 1hp, and could easily die to a cat (or basically anything that can deal damage). They had better odds in 3.5, given that they could deal two 1hp attacks per round instead of just one and a level one Commoner only had 1d4 hp, but in there Commoners are a leveled class and it wasn't clear how many were only level one.

Under no circumstances should a full grown human being have 1 max hp, thats just absurd. That is the house cat vs commoner disparity i mean.

Some people do, but I would say it's one of those things where you hear about it disproportionately often compared to how frequently it actually happens, since people are much more likely to write about negative experiences

Just kill me

It is expected that the gm will tweak things here and there for whatever reason, its part of their job. Its considered a major faux pas to look at monster stat blocks as a player.

One of the reasons I like Fate is it has tooling to avoid that kind of anti-climax without it feeling like an asspull. The BBEG is sitting in his office and the players, through hard work and planning, get the jump on him. Their first attack roll is net +8 stress. That's enough to kill almost anything! I as GM decide the BBEG is going to take a consequence ("Covered in Acid Burns" or whatever), and then *[concede](https://fate-srd.com/fate-core/conceding-conflict)*. Conceding is at the player level, not the character level. This is where you as a group decide on how the BBEG survives, but loses this scene. Maybe he teleports away, but leaves his computer unlocked. Maybe he drains the life force of his favorite second in command to save himself, damaging morale and loyalty. It's up to the group. Some people _hate_ this style of play, and want to be told a story rather then tell one as a group. That's fine. But it's hard for me to take off the GM hat, so I like when players also have a lot of say in the story.

Oh I love these collective storytelling systems as a gm, hate them as a player and though -- I wanna relax, pretend to be a person and explore the world, not think about what makes a better story.

Within the same campaign? Yes, I expect the statblock to be (reasonably) fixed. But from one campaign to the next? Not necessarily, unless they're explicitly set in the same setting.

I dislike FATE for exactly this reason - it breaks my immersion too much

My old DM said explicitly if he told us the monster's name in the MM he expected us to know it's stats, if he didn't then statblocks would be unreliable.