How do you handle monsters using social skills vs PCs?

I’ve checked the books and can’t find an answer by RAW other than the DM decides, so I’d like to know how people handle this in their games. What happens if a thug tries to intimidate/persuade the PCs? Do I roll vs the character’s skill (and which one) or set a DC based on how difficult I think it is? Most of the time I just describe the monster’s actions and let the players tell me how their character’s react, but the monsters have those skills listed in the Monster Manual for a reason.

What do you think is the best to handle these checks in order for the monster be effective, have the same fail chance as the PCs, and avoiding slowing down the play or making the players feel cheated?

Do monsters with a spellcasting trait get spell slots back after a long rest?

Some monsters, like a lich, have the Spellcasting trait. This trait allows such monsters to cast spells using spell slots, much as spellcaster player characters do.

However, taking the lich as an example, the trait does not mention how spell slots are regained (I’m ignoring their Lair Actions for the purposes of this question). Looking at the general rules on monsters’ Spellcasting trait in the Special Traits section:

Spellcasting

A monster with the Spellcasting class feature has a spellcaster level and spell slots, which it uses to cast its spells of 1st level and higher. The spellcaster level is also used for any cantrips included in the feature.

The monster has a list of spells known or prepared from a specific class. The list might also include spells from a feature in that class, such as the Divine Domain feature of the cleric or the Druid Circle feature of the druid. The monster is considered a member of that class when attuning to or using a magic item that requires membership in the class or access to its spell list.

A monster can cast a spell from its list at a higher level if it has the spell slot to do so. For example, a drow mage with the 3rd-level lightning bolt spell can cast it as a 5th-level spell by using one of its 5th-level spell slots.

You can change the spells that a monster knows or has prepared, replacing any spell on its spell list with a spell of the same level and from the same class list. If you do so, you might cause the monster to be a greater or lesser threat than suggested by its challenge rating.

There is no mention of spells slots coming back on a long rest. Elsewhere in the general rules, this is explicitly mentioned for other traits (such as X/Day traits):

For example, "1/Day" means a special ability can be used once and that the monster must finish a long rest to use it again.

It’s reasonable to assume that monsters with the Spellcasting trait do probably get their spell slots back on a long rest because that’s how it works for PCs, but on the other hand, monsters and PCs don’t necessarily use the same rules. So, does anything explicitly state that monsters with the Spellcasting trait get their spell slots back on a long rest?

Are there any monsters that can target more than one target/creature?

I noticed that the attacks in Statblocks mention one target (and sometimes one creature). This made me curious. I have been pouring over the MM and VGtM, but have not found any monster that can make a melee/ranged attack against more than one target / one creature.

  1. Do we know of any example within the ‘official’ books where this is more than one?
  2. If it’s always one, do we know of any reason why this is at all mentioned in the statblocks?

Related: Are there any issues with creating creatures that can make multi-target melee attacks?

Related: In the descriptions of monster action options, what's the difference between "one target" and "one creature"?

Do legendary actions trigger effects that happen at the beginning of the monster’s turn?

Consider this scenario. The monster is standing in the area of the cleric’s spirit guardians. As written, the monster takes damage at the beginning of its turn as long as it’s standing in the field. Suppose, however, that the monster takes a legendary action before its turn in initiative order. Does this trigger the effect of the spirit guardians, in addition to the normal trigger that would happen at the beginning of its regular turn? My ruling on the matter during the game was that it did not… This would seem to violate the whole purpose of legendary actions, resulting in a massive debuff of the monster (i.e. taking double spirit guardian damage simply because it took another turn in the initiative order).

Do monsters with the “Telepathy” language automatically sense creatures in their telepathic radius?

Some monsters possess the special “Telepathy” language.

Telepathy Telepathy is a magical ability that allows a monster to communicate mentally with another creature within a specified range. The contacted creature doesn’t need to share a language with the monster to communicate in this way with it, but it must be able to understand at least one language. A creature without telepathy can receive and respond to telepathic messages but can’t initiate or terminate a telepathic conversation.

A telepathic monster doesn’t need to see a contacted creature and can end the telepathic contact at any time. The contact is broken as soon as the two creatures are no longer within range of each other or if the telepathic monster contacts a different creature within range. A telepathic monster can initiate or terminate a telepathic conversation without using an action, but while the monster is incapacitated, it can’t initiate telepathic contact, and any current contact is terminated. (MM p.9)

Does this ability allow them to sense the position of all creatures within the radius of their telepathy, given that “A telepathic monster doesn’t need to see a contacted creature”?

Does a monster’s AC change when it doesn’t use its shield?

Every monster has a specific AC in its stat block. The rules don’t explicitly say anything like “subtract 2 from AC if the creature doesn’t use a shield”, do they? Does that mean a monster always has a fixed AC number regardless of the situation, even when it doffs the shield?

For example, the Goblin statblock says:

Armor Class 15 (leather armor, shield)

A goblin attacks with a shortbow. Since a shortbow is two-handed, the goblin can’t wield a shield at the same time. Should a goblin archer’s AC be 13 without a shield, or is it still 15?

What DnD 5e build (with minimum number of combined levels over all classes) is needed to summon all summonable monsters?

What build would make if you just want to be able summon all monsters (of the summonable monsters) without a general purpose spell like wish or special equipment – how many levels of a multiclass do you need at minimum? Specify background. I believe a Wizard (Summoning school) can nearly summon all monster types with CR limits but for instance has to choose between demons and animals at level 4.

Two target attacks from monsters

If a monster has an attack with two targets. Do I make a separate attack roll for each player, or do I make one attack roll and compare to each AC individually?

The monster in question , from A Wild Sheep Chase, has the following stat:

Whirling Greatsword Melee Weapon Attack +5 to hit, reach 5 ft. Two seperate[sic] targets. Hit: 10 [2d6+3) slashing damage.

Which monsters should be suggestible?

I am fairly new to DM-ing and I started a campaign with friends who are also more or less new to RPGs.

One of them has high Charisma and proficiencies in basically all abilities related to suggesting and influencing, and he tries to act on it on more or less every monsters they are running into. For example, last session, they came across Giant Crabs and his first reaction was to “try to intimidate them”, and then again trying to look friendly with Elks and finally trying to speak and scare off an Owlbear.

He seems a bit frustrated that this does not yield any result, and I would like to reward his ideas and his roleplay, but basically all these monsters are “non-intelligent” and don’t speak any language, and I feel that Charisma checks have no chance to do anything.

Edit (to keep with the originally intended question) :

What kind of monsters can PC “interact with” or influence ?