[RPG] Are PCs able to appraise the difficulty of an encounter

dnd-5eencountersforgotten-realmsgm-techniques

Are PCs able to judge, innately or via some skill check, how difficult a fight will be?

My assumption is that the adventurers have some knowledge of certain beasties and baddies, and can understand the inherent danger of the situation at hand.

I've never fought a lion in real life, and I don't know its AC or HP — but I can assume it will go badly for me. My players aren't super-experienced in the lore of D&D, so they might not have a clue what an owlbear is like or how dangerous a Rakshasa can be.

Part of the responsibility here as a DM is to throw manageable encounters at them — usually — but there are times when you want something trivial, or something impossible.

Can they ask, or should I signal "this is a deadly encounter", "this seems trivial", "this seems manageable"? Should they roll for it?

For the sake of this question, lets just limit this to the Forgotten Realms, and the world that revolves around the official wizard adventures.

Best Answer

Mechanically, there are a few ways.

The Fighter has a "Know your Enemy" class feature (PHB 73):

Starting at 7th level, if you spend at least 1 minute observing or interacting with another creature outside combat, you can learn certain information about its capabilities compared to your own. The DM tells you if the creature is your equal, superior, or inferior in regard to two of the following characteristics of your choice:

These choices include Strength, Dexterity, AC, HP, and class levels.

Moreover, you can call for various intelligence checks to determine how much a character knows about a creature. For example, (PHB 177-178, emphasis added):

Your Intelligence (Arcana) check measures your ability to recall lore about spells, magic items, eldritch symbols, magical traditions, the planes of existence, and the inhabitants of those planes.

Your Intelligence (Nature) check measures your ability to recall lore about terrain, plants and animals, the weather, and natural cycles.

As a DM, you have other tools.

By using these abilities and checks, characters might be able to glean some insight into how powerful an enemy might be.

However, other times PCs have no idea how strong a particular creature might be. For example, a plainclothes person with a satchel might be a commoner, or a powerful archmage--both could look identical in appearance, and you'd only know the difference once you fought them.

If you want to telegraph something non-mechanically, you can do so with context: a lair that's full of dead birds might not be threatening, but a lair full of the bones and armor of adventurers might be. Likewise, if there is advance notice, the characters can choose to do research on the creature in question.

Ultimately, as a DM, I use a mix of these strategies: sometimes, I let the characters make a check to know that a particular fight will be easy or hard, sometimes, I give the players no clue as to how strong a creature is, and other times, it's patently obvious (e.g. a giant flaming balor).

Probably the summoned monster doesn't count toward the challenge.

Bear in mind there's no RAW that specifies this, and challenge ratings of published monsters include some degree of "eyeballing" from the writers. But we can extrapolate a bit by using the basic challenge evaluation from the DMG on the stats that we do know.

I used Monstermancer* to run the stats of the Drow Mage without the summoning ability, counting all of its spells, and came up with a baseline challenge of 7:

"eval": {
    "defCR": 0.5,
    "offCR": 15,
    "dmg": 126,
    "ac": 15,
    "hp": 45,
    "atk": 6,
    "svDC": 14
}

So, without any eyeballing or special tweaks to its challenge evaluation, the Drow Mage's challenge matches the one given in the Monster Manual (in fact, this might be a little low, since it doesn't factor in the possibility of having an ongoing cloudkill spell active while throwing lightning bolts, but I digress).

However, while it looks like the summoned creature isn't "baked in" to the summoner's challenge rating, there isn't much guidance as to how you should incorporate it into an encounter. It's less effective than a full-fledged combatant for a few reasons (it takes an action to summon, it might not always succeed, &c.), but adding a challenge 4 shadow demon to a fight against a single challenge 7 mage is not a minor impact on the encounter, so it should count for something.

For a little more circumstantial evidence, there are variants listed in the Monster Manual for demons and devils which can summon other demons and devils; there is an entry for each type of fiend and which others they can summon with a percentage chance, similar to the ability of the drow mage cited here. These variants don't mention a change to the fiends' challenge ratings. Since the book doesn't assume a difference in the creature's own challenge with or without the summon ability there, it follows that the summoned creature should count separately in some way (even if not as a full-fledged combatant).

*Caveat: Monstermancer isn't perfect at this stuff, but it's an OK starting point. Also, there's a huge mismatch between the offensive and defensive challenges it gives to the Drow Mage, so it's a lot easier to take out than its challenge rating implies.

[RPG] Are there any mechanics to guess CR or learn encounter difficulty in-game

Yes, and maybe

The use of "CR" is an out-of-game term and there really isn't a way to learn that specific value using in game rules.

But what you may really be asking about is whether it is possible to gauge the difficulty of a fight before going in. There are two possible answers to this:

Yes, a Battlemaster Fighter or Mastermind Rogue can (functionally)

Battlemaster Fighter

The 7th level class ability Know Your Enemy grants you (PHB, 73-74)

Starting at 7th level, if you spend at least 1 minute observing or interacting with another creature outside combat, you can learn certain information about its capabilities compared to your own. The DM tells you if the creature is your equal, superior, or inferior in regard to two of the following characteristics of your choice: [Strength, Dexterity, Constitution, AC, Current HP, Total class levels (if any)]

Mastermind Rogue

The 9th level feature insightful manipulator provides a similar ability(Xanathar's, 64):

Starting at 9th level, if you spend at least 1 minute observing or interacting with another creature outside combat, you can learn certain information about its capabilities compared to your own. The DM tells you if the creature is your equal, superior, or inferior in regard to two of the following characteristics of your choice:

Intelligence score

Wisdom score

Charisma score

Class levels (if any)

At the DM’s option, you might also realize you know a piece of the creature’s history or one of its personality traits, if it has any.

Your DM should communicate with you

Depending on your level, you are a seasoned or somewhat seasoned adventurer. A DM could provide a basic gut instinct on creatures/scenarios they expect you to engage in or expect you to be wary of. However, there may be times where you want to take the risk or forego an easy win that may complicate this.

My table (and also suggested by W.Gering), often allows for a searching of player knowledge vs a history/arcana/nature/religion type check (depending on the monster type.) Setting a DC for various levels of knowledge is an option for you and your players.