How can PCs estimate the power of opponents? [duplicate]

Question

It's common for players to assume that opponents are always “level appropriate.” However, mixed level modules change this situation. Recent modules like Tomb of Annihilation can have PCs stepping into areas far beyond their skill.

This raises the question though: what in-game ways to the PCs have to estimate the power and capabilities of their opponents? If the PCs are an inexperienced level 1 party and meet a CR4 opponent where often one strike could kill a PC, not knowing this could be a total party kill.

(For the purpose of focusing this question, please ignore experienced players who know the contents of monster manual or who have gained out-of-character information they can use for judging enemies. Besides, even that often doesn't work for NPCs with class levels!)

I'm not looking for how the DM can hint at NPC/monster power — those are DM techniques. I'm looking specifically for what mechanics and rules players can use to have their PCs gauge the power of an opponent — whether that might be hit points, CR level, stats like strength, talents or magical abilities. How can PCs judge the opposition's strength?

Answer 1

Here are the rules (PHB p.6):

How to Play

1. The DM describes the environment

The challenge of the creature before them is part of the environment so it is incumbent on the DM to describe it. How they describe it is up to them.

However, subtlety is not your friend!

Real people in the real world have a whole range of senses, in-world knowledge, experience and expertise to bring to bear consciously and unconsciously when assessing a threat. Their bodies have a whole automatic physiological, emotional and psychological systems that kick in before they consciously realize there is a threat to be assessed. They also have the real prospect of physical harm or death to heighten that response rather than the lower stakes of having to roll a new character.

The players at your table have ... you. You are their sole interface with the world - if something is scary threatening then you need to tell them exactly that.

Different DMs will have different styles ranging from “This guy is CR 36” through “This is a deadly encounter” to “As he speaks you hear the icy tones of a killer. Your pulse starts racing, your mouth goes dry and your palms sweat. Choose your next action carefully: your life depends on it.”

Answer 2

The previous two answers haven't mentioned some skills which should be relevant:

Perception

This skill should detect big danger signs. Perceptive PCs should realise when they are moving towards a serious confrontation.

They detect large claw marks on the bark of trees, scent the foul odour from piles of faecal droppings, notice an indentation in the ground is actually a huge footprint, hear the nocturnal grunts from a hunting pack trailing them, and so on.

Unperceptive PCs should miss these hints, and a party of unperceptive PCs should end up over their heads in difficult encounters on occasion.

Investigation

This skill check should help PCs judge encounter difficulty. Investigation should pick up subtle clues about foes.

Does the half-orc chieftain carry a staff festooned with dangling ears from previous victims? Good Passive Investigation or a high roll on active Investigation also picks up a belt with several pouches stuffed full of ingredients and a sharp, blood-drenched knife, likely used to take the trophies on the staff, indicating the chieftain is a spellcaster of some sort who has personally killed a lot of enemies.

Insight

This measures intentions, which can all sorts of use in determining how difficult a foe might be to fight.

Good insight should indicate whether the bandits are stone-cold killers or a rubbish band from the nearest village looking for a quick payoff, the wizard has a hair-trigger temper, the giant lion has just eaten or is currently quite hungry, or the bear is a protective mother.

Other skills such as Arcana, History, Nature, and Survival can also assist by allowing characters to recognise dangerous creatures and their oft-told powers (such as the legendary petrification power of a medusa, who was defeated by the hero with the mirror shield) due to information gleaned from myths, tomes, and mentors.

The players should be using these skills to judge encounters. If they aren't, then they should take it on the nose a few times until they realise these skills exist to be used. Characters that focus on such skills should have opportunities to shine, such as saving the party's bacon by knowing when to retreat or avoid an encounter.

Answer 3

This can be a tricky problem, but some solutions can be found in vivid descriptions:

"One of the bandits, however, looks older. He is scarred all over, and, on closer look, you can see that some of the scars are tally-marks."

"The Orc in the center, however, is huge. Beyond huge. You never really knew they made Orcs in this size."

"Just looking at this man, you know he's very, very good at his job, and his job is killing people."

Answer 4

Be a Battle Master Fighter

The only way to force your DM to give you quantitative information on enemy strength is to use the Battle Master's Know Your Enemy feat:

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 options include things like AC, HP, and class levels.

Ask a lot of questions

Beyond that class feature, knowing the strength of an enemy is going to be up to your DM. They are the ones who control all the descriptions, and if they want to hide an enemy's strength from you, there's not that much you can do about it.

However, you might be able to know something by asking the right questions. The go-to question I ask is, "Do I know anything about this creature?" Asking this usually prompts my DM to call for some kind of INT check (arcana, nature, etc.). Depending on the roll, the DM then gives me some information about my potential enemy, which lets my party gauge difficulty.

Barring a direct question, you can also ask about specifics. Detect Magic, for example, will help: a fully mundane human is likely weaker than one decked out with magical items. Likewise, you can examine the creature's surroundings to glean information: a bunch of T-Rex bones in a creature's den might indicate that the creature is quite strong.

Answer 5

Class Abilities

• Rogue, Mastermind, Insightful Manipulator (subclass feature) allows you at 9th level (outside of combat) to gain information on two of a number of options of your choice (class levels, and each of their mental ability score statistics) [XGtE]
• Fighter, Battle Master, Know Your Enemy (subclass feature) allows you at 7th level (outside of combat) to gain information on two of a number of options of your choice (total class levels, fighter class levels, each of their physical ability score statistics, Armor Class, and Current Hit Points) [PHB]
• Fighter, Arcane Archer, Seeking Arrow (subclass feature), can learn creature's location, for a creature you have seen in the past minutem if they are in range and the target fails their Dexterity saving throw. [XGtE]
• Ranger, Monster Slayer, Hunter's Sense (subclass feature), as an action you can learn if the creature has any damage immunities, resistances or vulnerabilities and what they are. [XGtE]

Spells

• Various charm type spells (Charm Person/Suggestion), to get the thing to tell you whether or not they think they are better than you
• Commune Spell (yes/no/unclear to three questions [or short phrase as appropriate] from a Diety), 1 min casting time
• Contact Other Plane Spell (5 questions, 1 one word answers [or short phrase as appropriate] from an extraplanar being), 1 min casting time, potential of going insane
• Divination (1 question relating to a specific goal, event or activity in next 7 days, turthful answer from DM), 1 action to cast
• Speak with Animals (get to speak with animals to get their impressions of a creature, probably unreliable info)
• Speak with Plants (specifically says you can get info about creatures that have been in the spells area in the last day from speaking with plants)
• Wish (depends on how you word it, but probably a waste of a wish)
• Detect Thoughts (potentially get creature's strategy, or deeper information with a probe, but they know you have dug around if you probe deeper)
• Identify (Can learn if any spells are affecting a creature by touching it), 1 min casting time

Other possibilities

• Wisdom Checks (to learn if a creature is undead)
• Insight Check (to get a gut feel for the creature)
• Listen carefully to the DMs description
• Talk to people who have been in contact with the creature before
• Research creature (if you have enough time)
• Sage Background, Research feature (to recall something you have researched, or where you can find it)
• Arcana checks for spellcasters (as they may have read about the creature in the past)
• History check for others (as they may have read about it in the past)
• Nature/Survival checks for Rangers against their favoured enemy
• For Legendary creatures the character may already know some rumours/information about the creature (eg Dragons are super dangerous creatures!)
• Druids may know some information due to their Wildshape ability/close connection to Nature