Knowledge Skill: Monster Lore

You can use this skill to identify monsters and their special powers or vulnerabilities.

Check: In general, the DC of such a check equals 10 + the monster’s CR. For common monsters, such as goblins, the DC of this check equals 5 + the monster’s CR. For particularly rare monsters, such as the tarrasque, the DC of this check equals 15 + the monster’s CR or more. A successful check allows you to remember a bit of useful information about that monster. For every 5 points by which your check result exceeds the DC, you recall another piece of useful information.

When the players's characters meet a creature, the GM (or the players) could ask for a Knowledge skill check. Normally, people will first roll the dice and then ask what skill they should use, as it varies from monster to monster. The higher the result, the more information they recall about the creature.

The GM either has to look up the monster's stats and consider what could be useful on that situation and worth recalling for the character. Or ask the player what he would probably remember about the creature. The later is prone to metagaming, and the player could ask for things the monster might not have (a tiger has no vulnerabilities).

The GM should be careful to not give out information that is already obvious to the characters. An orc wielding a two-handed heavy axe that you identify that it is certainly a battle-axe and not a handaxe is not an useful piece of information in any form or shape, as that hardly helps against that orc.

Equipment is usually descriptive when you describe the encounter or the actions taken by the enemies. If said orc seems like he is wearing a breast plate with leather scraps, then that's probably a given that is is wearing a breastplate as his armor and will probably have at least 16 AC.

What you shouldn't give out as information:

• Any mechanical game stats;
• The previous item covers attack bonus, AC, hit points, hit die, saving throws, DC for abilities, how their special abilities work, their prepared spells, their known spells (*), their equipment that is not obvious to see, the amount of gold they are carrying in their pockets.

Let me just add that nothing stops you from giving out a creature's stats, but you don't have to, there are no rules saying you should. I know that some GM's prefer to hand out stats, but that moves the game a bit from a roleplaying game and more towards a tabletop game.

"*" If the creature has a known spell that is at will or that the creature is known for using it often, then that might be ok. Such as a blinking dog teleporting around at will or an imp that is nearly always invisible outside of combat.

What is a good narrative information that you could give them:

• The name of the creature. That should be the first thing identified.
• Rarity of the monster. Is he normally seen around there? Is he from another place? Is it normally summoned? Normally, describing the Environment information from the bestiary is enough (this is a beast normally seen on cold mountains, what brings her to this forest, nobody knows...).
• General information about the creature, this is usually the first few paragraphs of text about the creature, this might be even more informative to the characters than saying that the creature has this or that special ability.

• Gnolls are a race of hulking, humanoids that resemble hyenas in more than mere appearance; they show a striking affinity with the scavenging animals, to the point of keeping them as pets, and reflect many of the lesser creatures' behaviors. Gnolls are capable hunters, but are far happier to scavenge or steal a kill than to go out and track down prey. This laziness impels them to acquire slaves of whatever type is available, whom they force to dig warrens, gather supplies and water, and even hunt for their gnoll masters

• Make up a legend their heard about this creature before, and that's how they knew about it (The dreaded ghasts of the Moonscar River). If the character is a wizard or has invested a good amount of skill points on that knowledge skill, you could make up the name of the book their read it from (The Tale of the Green Manticore).

And there are things you could say without any knowledge check, such as:

• The header text on the bestiary, yeah, the one in italics, that is usually a good descriptive text for someone who has never seen this creature before.

• This walking corpse wears only a few soiled rags, its flesh rotting off its bones as it stumbles forward, arms outstretched..

• What weapon they are wielding, if it isn't an exotic weapon.
• What seems to be their armor, if a player asks. You don't have to say what armor it is specifically, but a general idea is enough. Leather armor, leather scraps, leather armor with bits of metal on vital areas, a huge plate of metal covering their chest, etc.
• Everything that you could tell simply by looking at an image on the creature (big teeth, long tail, green fur, glowy red eyes, four arms with claws, etc).

What is a special ability or vulnerability then?

This one is actually easy to answer. Look up a monster's stats. Read it thoroughly.

Now, what is the first thing that comes up when you think about it. That's the relevant information!

If the creature is a dragon, this is usually their dragon breath, their powerful spells, their high intelligence, or their frightening aura. If the creature is a ghoul, that should be their disease and paralyzing touch. If the creature is a succubus, that should be her charming and polymorphing powers. For a troll, that would be his regeneration that makes them immortal if fire is not used to burn the wounds, and so on.

Just keep in mind that this is an information that the character remembers. So he read or heard about this creature before, or a creature similar to the one he is looking at (or listening about). So, you have to think what about be something they would remember, what stands out most, what would make them scared of this creature.

Some facts about a medusa are completely irrelevant when you know that she can turn you into stone if you look into her eyes. Like, who cares if her bite is poisonous?, a lot of creatures are poisonous, but few of them can petrify you.

A vulnerability example is how trolls can be hurt by fire and acid.

Some creatures will have no special abilities, but their defenses or regenerative powers makes them strong. Knowing how to prevent their regeneration is something more useful to know than how much their bite hurts

Knowledge checks are not an action

This is exactly what the rules say. You don't have to waste an action to make a knowledge check, not even a free action. Which means you can make the check even when surprised and it's not your turn.

That doesn't mean you should tell the player everything about the creature before the combat even starts. Otherwise you might see some bad metagaming from the other players who just heard this information before the character that knows it even had the chance to speak.

Normally, it's good practice to wait for the character's turn before describing the result of his roll. So, after hearing what he knows about it, he can tell others on his turn using his free action to speak.

Improvised Weapons are not a subset of Melee or Ranged Weapons, but they are Weapons.

Let's begin with the identification of the Improvised Weapon as a Weapon (and not an object or Armor, or anything else). Jeremy Crawford supports this:

An improvised weapon is, indeed, a weapon, but only the moment it's used as such. A chair/shield/etc isn't a weapon otherwise.

What type of weapon is it? An Improvised Weapon

Chapter 5 of the PHB (page 149) contains a list of common Melee and Ranged Weapons. That is the list for things that require Melee Weapon or Ranged Weapon attacks. Existing items within the ruleset that are not listed here would likely not qualify, but items that are not listed which have similarities would (i.e. katana as longsword). A shield is not on the list, but is under Armor.

Whether or not Improvised Weapons are on the list is the exact question being asked here.

Jeremy Crawford takes a bit about the object vs process here:

In D&D, a weapon is an object. A weapon attack is a process. Sometimes the rules let you use nonweapons to engage in that process

An Improvised Weapon is neither a Melee Weapon nor a Ranged Weapon (from the list previously defined on page 165.) It is it's own category that can be found pages 147-8 in the PHB.

Type of Weapon is different from type of Attack

While you may make a Melee or Ranged Attack with one, it does not turn the Improvised Weapon into a Melee or Ranged Weapon. It is just a Melee or Ranged Attack that is made with an Improvised Weapon.

Crawford covers this in the following exchange:

A melee weapon attack is a melee attack with a weapon.

and the following exchange with a user (the first quote):

@Sebkha Not to be confused with: an attack with a melee weapon.

@JeremyECrawford That's correct, since an attack with a melee weapon can be a ranged attack if you throw it

Proficiency points the way towards a different Type than Melee/Ranged

If an Improvised Weapon is ALWAYS either a Simple or Martial Melee or Ranged weapon, then there would have been no need for this clarification on proficiency in the Improvised Weapons rules:

In many cases, an improvised weapon is similar to an actual weapon and can be treated as such. For example, a table leg is akin to a club. At the DM’s option, a character proficient with a weapon can use a similar object as if it were that weapon and use his or her proficiency bonus.

If it was a given that an Improvised Weapon was always a Simple or Martial Melee/Ranged weapon, then proficiency would always apply. In addition, the only way to gain proficiency in an Improvised Weapon is through the Tavern Brawler feat. This would be unnecessary if Improvised Weapons were classed as part of Melee/Ranged as your proficiency would already be granted if that was covered by your race/class.

Crawford discusses this a bit here:

A shield certainly isn't a weapon, but like many things, it can be used as an improvised weapon.

There is clearly a differentiation in Crawford's eye between Weapons and Improvised Weapons.