Identifying a Monster in D&D 5e: More than an Intelligence Check.
Updated: Apr 25
You've probably experienced an encounter where a player asks, "Do I know anything about this monster?" Knowing what specie or type of creature you face – its hit points, traits, abilities, and attack options – is valuable in combat. But 5e rules don't provide a straightforward answer to this question.
1. BASIC APPROACH
Requiring a lore-based Intelligence check (see Player's Handbook p. 177) is one way to do this. Chris Perkins suggests this. A number of DMs have done a nice job systemizing this approach by linking particular lore-based Intelligence checks (Arcana, History, Nature, and Religion) to particular monster types: aberrations, beasts, celestials, constructs, dragons, elementals, fey, fiends, giants, humanoids, monstrosities, oozes, plants, and undead (see Monster Manual p. 6).
More recently, Tasha's Cauldron of Everything (p. 148) provides a "Monster Research" table that provides for each monster type a suggested skill or skills that could reflect knowledge of the monster type. These skills include the four lore-based skills and the Wisdom-based skills of Animal Handling and Survival. The table provides the following:
Beast: Animal Handling, Nature, Survival
Celestial: Arcana, Religion
Dragon: Arcana, History, Nature
Elemental: Arcana, Nature
Fey: Arcana, Nature
Fiend: Arcana, Religion
Monstrosity: Nature, Survival
Ooze: Arcana, Survival
Plant: Nature, Survival
Undead: Arcana, Religion
The table works like this: You encounter a monster of the Aberration type. The DM has you roll an Intelligence check to see if you know anything about the monster. You have the Arcana skill. Since Arcana is a listed skill in the Aberration entry, you add not only your Intelligence modifier to the roll but also your proficiency bonus. The Difficulty Class will depend on the creature's challenge rating, the rarity of the creature type, and other factors.
The table is a starting point. Depending upon the situation, a skill not listed with the monster type may nevertheless be relevant to identification of the creature type in question. The following are just a few examples of this situation. Common sense should prevail.
Religion may help in identifying creatures with prominent religious or cultic practices (e.g., kuo-toa).
History may help in identifying creatures associated with an ancient or lost kingdom.
Arcana may help in identifying creatures with prominent magical abilities.
2. BEYOND THE BASIC APPROACH
If you like more realism, so to speak, in the game and appreciate context, consider modifying the basic approach as follows.
When asked if a character knows anything about an encountered creature, the DM first makes one of the following threshold determinations:
There is no in-world justification for you to even have a chance of knowing anything about the creature encountered. No ability check is allowed.
There is an in-world justification for you to make an ability check. In certain circumstances you may be granted advantage.
You are simply deemed to have knowledge of the creature type encountered. This is because of your particular background, race, character class, or other defining characteristic has a link to the creature type in question. No ability check is necessary.
Rodney Thomson says that he would be "more inclined to allow a check if there is an in-world justification beyond 'I have a high Int.'" Mike Mearls states: "I don't allow checks for weird creatures that a PC couldn't have possibly heard about." These are good points. Sometimes a die roll shouldn't be able to change fundamental limitations of a character.
How do you determine if there is an in-world justification for a character to make a creature identification check? You consider the specifics of the character and the type or specie of the creature encountered.
Here are some factors to consider:
Background. Given the character's background (PHB p. 121), is it likely that the character when young heard stories from elders about this specie of creature?
Race. Does this specie of creature figure prominently in the lore of the character's race? An elven adventurer likely knows something about the drow.
Language. Does the creature have a unique native language and does the character know it? If yes, the character likely knows something about this specie of creature.
Character Level. All else equal, the higher the level of the character, the more likely the character knows something about the creature specie in question.
Character Class. Does the character's class suggest likely familiarity with this specie of creature? Possible affiliations include:
Barbarian: creatures found in the wilds (tundra, jungle, forest, mountains, plains, desert, etc.) of the barbarian's homeland.
Cleric: celestials, fiends, and undead.
Druid: beasts, fey, elementals, plants, and oozes.
Paladin: fiends, undead, and, if the Oath of the Ancients (PHB p. 86) is taken, fey.
Ranger: beasts, monstrosities, giants, dragons, and favored enemies.
Sorcerer: creatures of the same monster type as that of the sorcerer's source of power.
Practitioners of necromancy: undead.
Warlock: creatures of the same monster type as that of the warlock's patron.
Wizard: aberrations, celestials, constructs, dragons, fey, fiends, elementals, monstrosities, undead, creatures of other planes.
In certain circumstances, the factors in the table could lead a DM not only to allow an ability check but also to grant advantage on the check.
Sometimes it make sense for the DM to conclude that you simply have knowledge about the encountered creature. In other words, no check would even be necessary.
For example, I would rule that a high-level cleric or high-level fighter will simply know that a skeleton has damage vulnerability to bludgeoning damage. This approach is essentially an enhanced version of the "Background Proficiency" variant rule in the Dungeon Master's Guide (p. 264).
3. IS AN ACTION NECESSARY?
Another issue is whether you get to identify an encountered monster for free or need to expend an action. I think you would not have to use your action in order to identify a creature.
You're not attempting to actually do something here, but rather, are simply asking the DM about your current state of knowledge. You either know something about the creature or you don't.
Note that we are not talking about engaging in the act of investigation. If you didn't already know something about the creature but wanted to examine it and try to logically discern from what you observed the creature's abilities and features, then you would have to use an action to make an Intelligence (Investigation) check.
This is because of the time you would spend in taking in the visual and possibly other sensory data and in intellectually processing the data. Matthew Mercer has taken this approach.
The context-rich in-world approach in handling the identification of creatures is more fair and interesting. Success is steered away from an over-focus on Intelligence. Book knowledge is not everything. A seasoned high-level fighter with a low Intelligence score will know more about the potential threats lurking in the world than the most brilliant, low-level wizard.