I haven’t played much dnd, do people expect stat blocks to be fixed? Like, is meta knowledge such a part of the game that its a dick move for gm to change it?
Meta kills some kinds of fun and, for lack of a better term, can be like topping from the bottom. If you’re trying to keep it out of your game with this method, your group is dysfunctional either because there are misaligned goals or the gm and players are in a pissing contest.

Im not really asking from a power-dynamics standpoint, more as a narrative tool. As a gm I change the world to make what I see as a better story (no cheating necessary I’m literally the universe).

Like, if the players do an ambush of BBE and (according to the rules) one-shot ‘em, he’d have a shielding amulet leaving him heavily maimed but alive. Not cause how dare you kill my beautiful npc, it’s just kinda anticlimactic otherwise.

(Unless the ambush was a huge challenge in itself. Then we’re good, murder away)

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.

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.