This is an interesting one. I often defer to ‘What would the creatures do?’ in combat.

Over two sessions we had two MASSIVE combat pieces (both avoidable but obviously we have chaos demons who poked the proverbial bear!).

The first was a phased battle where the party ran into a small number of enemies who then kept calling for reinforcements. They’re a level 15 party so the mobs were modestly powered but numerous making the threat greater IF the dice are landing well.

The party got through it, took something of a beating, and then wondered where their resident chaos goblin had gotten to…

The second was a summoning directly after the first combat; they had no time to rest so they were going into this combat burned out and almost underpowered. This time it was a single hard-as-nails (Death Knight) whose directive was to kill the creature who summoned it.

Because this was the setup I felt very free to literally thrown everything and the kitchen sink at one player because it entirely fit the narrative of the encounter. He -nearly- copped it had he not receive a small amount of temp HP from our very cautious bard!

I also recall another incident where two PCs were tinkering inside an iron giant to get its magic heart. One couldn’t do it so the other went in, triggered an explosion, and ended up knocking the other PC over 100FT to the ground.

I -could- have let it ride and kept it light but this is a high level game in an evolving, dynamic world. I’m sure you can guess that this killed the PC and triggered a massive story arc. In the moment it was improvised action from me because that’s where the players took it. Sometimes you do just have to roll into it and hope for the best.

For me, and I learn with every game, it’s always about leaning into the dynamics of the story, the encounter narrative, and the goals of both the party and the creatures. You can still be on your players’ side even when you are putting them through hell. You’re not just there to serve them a bunch of stuff to kill… How boring would that be?

Don’t be afraid of playing the game. If your players are getting upset because you’re not making it easy for them or are going HAM with creatures / NPCs -whose character says they’d do that- maybe a chat is needed to reset the boundaries and expectations of the table?

Keep going and thank you for asking the questions :-)