Knowledge Checks
Exploring the mysterious world, adventurers could know quite a bit about the creatures who reside in their worlds, far more than the players might. When presented with a strange monster, a character can take a quick second to jump through the various monsters they have learned about, trying to recall from ancient tales what a creature might be weak against, how to bring a monster down, and even where they hail from.
Appropriate and Unique Monsters
Not every monster is it appropriate to know random tidbits about them. It could be an ancient elder evil from across the stars, whose very form is chaos incarnate. Being able to accurately recall what the ancient evil is capable of might be impossible simply because it has never touched the world before, making it so no one knows anything about it. On the other hand, kobolds are relatively common creatures and it would be very appropriate to try and recall their weakness to sunlight and their propensity for tricks and traps.
Unique monsters, unless they have been written down in ancient tomes, can not be rolled on to see what an adventurer knows. The DM has the final say on what creatures are unique, what creatures are rare, and what creatures are common enough to make knowledge checks on.
Making a Check
Depending on what type of creature you are facing, the required skill is going to change. It doesn't matter if you know everything about the natural world and the beasts who populate it if you are facing down a horrifying demon. Then again, it might make sense to use your knowledge of the multiverse and the Outer Planes to determine what a celestial beast is capable of. The following chart below has recommendations on what skills are required based on the creature type, though many of these could overlap or be different depending on the creature you are fighting.
Recalling information on a Star Spawn is typically an Intelligence (Arcana) check, but a cleric might know about them as they are often accompanied by religious cults. In that instance, the DM may allow that player to roll an Intelligence (Religion) check instead, adjusting the information as needed.
Rolling this check does not require an action.
Skills & Creature Types
| Skill | Creature Types |
|---|---|
| Intelligence (Arcana) | Aberration, Construct, Dragon, Elemental |
| Intelligence (Nature) | Beast, Fey, Giant, Humanoid, Monstrosity, Plant |
| Intelligence (Religion) | Celestial, Fiend, Ooze, Undead |
Difficulty of the Check
Not every monster is as well known as others, and some may have only a few scant documents in the entire world to learn about them. On the other hand, everyone knows that trolls hate fire and that therianthropes require silver.
The chart below provides a guide for the DM. They may decide that certain creatures have a higher base DC, or that something is so easy that it doesn't even require a check in the first place.
Useful Things
Every successful check also brings with it useful information about the creature, the DM can choose to provide what information they deem is pertinent or appropriate or allow the character making the check to ask what information they'd like. This useful information could include any of the following, or anything else appropriate.
- Creature Type
- Number of Hit Dice
- Type of Hit Dice
- Best/Worst Saving Throw
- Skills
- 1 Weakness (if any)
- 1 Resistance (if any)
- 1 Immunity (if any)
- Special Senses
- Special Abilities
- Special Attacks
- Number of Attacks
- Attack Damage Type
DC & Useful Things
| DC | Number of Useful Things Learned |
|---|---|
| 10 + half the creature's CR |
1 Useful Thing |
| 10 + the creature's CR | 2 Useful Things |
| For every 5 after | 1 Additional Useful Thing |
Optional Rules
Bonus Action Checks
Instead of being a free action to recall information about a monster, it could require a bonus action as the character must spend a few seconds trying to recall such information.
Insightful Checks
Sometimes, the best experience is watching a monster fight. A DM may allow a character to make a Wisdom (Insight) check to gauge a monster's physical or mental abilities, but the knowledge they learn is going to be far more limited than recalling research on a creature.
Proficiency Required
Certain monsters might require a character to be highly proficient in a specific skill to get anything useful on them. This could be tied to CR, like all CR 10 creatures and higher require a character to be proficient in that skill. This makes proficiency in Intelligence-based skills very important for those who want to fight monsters intelligently.
Research First
The DM may only allow certain monsters to be rolled on only if the character has spent downtime in a library or other place of learning. The DM may reduce the DC or provide advantage on creatures if a specific one is researched.