Medusa's gaze is not blocked
While not addressed well (or at all) in the books, in the official rules answers Sage Advice Compendium a test for whether something is magical is laid out. See here for the Sage Advice Compendium, or here if you which to stay on stack. In short, we have a five step test (numbering mine; there isn't really any order to them, but ...
Devils are immortal
In 5E, the Monster Manual entry on Devils has this to say:
Dark Dealers and Soul Mongers. Devils are confined to the Lower Planes, but they can travel beyond those planes by way of portals or powerful summoning magic. They love to strike bargains with mortals seeking to gain some benefit or prize, but a mortal making such a bargain ...
First, the general principle that answers most of these:
A monster's challenge rating is based solely on its own statistics
Does a leading dragon gain CR based on the number and quality of her servants?
Would gaining the spell power of an arch-mage (CR 12) add to her high-ranking CR? If so, how much?
No. If these servants or allies are involved in ...
CR is a purely metagame construct
Remember that Challenge Rating is purely a construct of a game. Within the fiction, a dragon wouldn't even know that it existed, much less seek to increase it directly.
In fact, while all the things you listed are controlled by CR within the game, that simply serves to give the DM an easy way to quickly create the monster ...
A Quori is not destroyed when it's host is
When we look at the stat blocks for the Hashalaq, Kalaraq, and Tsucora Quori, which are quori that do not currently possess a body, we see an ability called "Possession", which does just that, and includes the text
The possession lasts until the body drops to 0 hit points, the quori ends it as a bonus action, or ...
Most: Poisoned (434). Least: Incapacitated (1); Unconscious (26).
As of the writing of this answer, there are 1652 total monster/NPC statblocks listed on D&D Beyond.
We can use the filtering options in D&D Beyond's monster listing to see how many monsters/NPCs across all sources are immune to each condition:
This spreadsheet lists the number of monsters from the Monster Manual, Volo's Guide to Monsters, and Mordenkainen's Tome of Foes that are immune to each condition.
According to the spreadsheet:
The most creatures have immunity to the Poisoned condition
The fewest creatures have immunity to the Unconscious condition
And (based on my D&D beyond search) 1 ...
According to the written rules, no.
A dryad's Fey Charm action specifically says it
targets one humanoid or beast that she can see within 30 feet of her.
A yochlol is a fiend (and a demon and a shapechanger), not a humanoid or a beast, so it can't be targeted by the dryad's Fey Charm.
Practically, however, you can do whatever you want to make a good ...
The third Monstrous Compendium for Ravenloft, has a page referring DMs and players to other AD&D 2e products for the stats of various monsters. In the case of Imp, the stats are available in the Monstrous Compendium Volume 1. You can also find them in TSR 2140, Monstrous Manual.
Imps are diminutive creatures of an evil nature who roam the world and ...
They get bound in an object, then escape the object to enter a mortal soul
It says on p. 51 of the Monster Manual in the section on Bound Demons:
...ancient tomes describe techniques that can trap the essence of a demon... within a weapon, idol, or piece of jewelery...
and further on the same page under Demonic Possession:
No matter how secure its ...
The Beatings Will Continue Until Morale Performance Improves
It does exactly what it says it does. The Drow House Captain can attack an ally with the whip, and that ally gains advantage to attack rolls. The Captain is flogging subordinates in hopes it will make them fight better, and in this case, it actually works.
Note that the whip attack does not ...
The features stack because they do not have the same name
The section from the DMG states:
Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap.
- Dungeon Master's Guide (page 252; ...
Magical Effects that Aren’t Spells
Are there other (better?) ways for casters to damage this sucker before L7 slots are available?
I actually had a Paladin in such a predicament recently.
A Paladin’s Divine Smite power is a way to expend spell slots to damage a foe, but it is not a spell. Thus it can damage a Rakshasa.
Mike Mearls tweeted to this ...
: equaling an arithmetic mean
: being about midway between extremes
a man of average height
: not out of the ordinary : COMMON
on an average day
the average person
It’s not 1 because the average person has approximately 1 testicle and 1 ovary. Whereas any person picked at random is most likely to ...
For the purposes of the spell Familiar has a particular meaning (that given by the spell Find Familiar), but creatures with the Variant: Familiar trait are not actually familiars by that definition, so you can have both
The definition of what a familiar is in game terms (for the purposes of this spell at least) is (emphasis mine):
You gain the service of ...
From the description of the creatures ability states that it grants actual an hit dice increase, and there is no rule restricting accumulation of these. Since the hit dice are temporary, it can only stack so much at any given time. If these were temporary hit points, instead of actual hit dice, we would know that it does not stack, due to the Temporary ...
No, in every creature with the Shapechanger trait, its type stays the same.
A mimic is always a mimic; a werewolf is always a werewolf; a succubus is always a succubus. That is why they have abilities only usable in particular forms.
Consider the description in the stat block. For the succubus, the trait says:
Shapechanger. The fiend can use its action ...
For the purposes of being affected by effects, it depends on the creature
Depending on the creature, the shapeshifting ability usually describes which statistics are kept and which are not. For more details on what counts as statistics you can see this question. The statistics are what determines what a creature counts as.
For example, the werewolf states ...
I would say yes, a werewolf is a wolf in wolf-form and a mimic is the object. Not 100% sure though.
As far as i know they get affected after shaping like the object or form they shape into for example smashing in the case of the mimic.
First of all, this is a question only a DM can answer, because such a creature could also just be labeled as a plant, a monstrosity or anything else the DM feels like. But, there is a precedent!
The Druid of Spores from the Ravnica campaign setting has the ability to use its aura of spores to revive creatures that die as zombies. For all game ...
Besides the answers given I wanted to add another source for Rothé, a type of subterranean oxen used as cattle of some kind. The prologue to R.A. Salvatore's book Exile seems to indicate that the protagonist Drizzt kept these as a source of food:
The hunter watched the basilisk pass as he had watched it earlier that same day. The eight-legged monster was ...
The Forgotten Realms Wiki1 page for the drow contains a section on animals which list a number of different animals raised by the drow, including sources for where those animals are mentioned, in most entries and span several editions and different articles. Referenced animals include bats and dire bats, Cavvekans, Lizards, Rothe, shriekers, snakes, spiders.
The Drow raise spiders.
The Drow description in the Monster Manual states:
The drow raise and keep giant spiders to help protect their cities against intruders, even as they drape those cities in beautiful webbing, creating a gossamer snare to catch flying enemies that would otherwise soar over the walls.
Since they worship what is essentially the ...
Liches can remember their past life, but may also forget it with time.
According to Dragon Magazine #234's Bazaar of the Bizarre: Lich Magical Items, liches in their early stages are often saddened or distracted by memories of their past lives, such as now-dead loved ones. Their solution is to use a memory globe, a magic item which intentionally removes ...
I looked through several references relating to Lichs and most skipped the actual effects of becoming a Lich. However I did find this on the Lich Wikipedia page:
Unlike most other forms of undead creatures, the Lich retains all of the memories, personality, and abilities that it possessed in life
Unfortunately the page didn't have a citation for that ...
After considering all swallowing monsters I could find in all avaliable to me resourses, I found out two things.
1) Escape damage threshold is always a multiple of 10.
2) Creatures with higher CR have escape damage threshhold no less than creature with lower CR. No outliers here.
After fiddling with numbers I came to formula that covers all monsters from ...
I am going to reverse engineer this to suggest "it's a long shot" intent
For the sake of illustration, I'll use three martial characters (partially optimized) at level 11 who get swallowed in the first round. You offered up level ranges from 9-13, so I took the middle value. When you observe that
it seems very unlikely to me that an unoptimized ...
I think the DC is just 10 + the CON save modifier of the creature. The Remorhaz has a similar mechanic and the save for it is DC 15 and it has a CON modifier of +5.
As mentioned by Revolver_Ocelot in the comments, the Kraken has a CON save modifier of 15 even though it's CON modifier is only +7. The DC for it's swallow ability is 25. Oddly enough it's CON ...
What you have about Ki-Rin in Volo's Guide to Monsters and Celestials in the Monster Manual is all you've got. Neither indicates that Ki-Rin are immortal or give any indication of their life-cycle.
Ki-Rin have appeared in every edition of Dungeons & Dragons except 4th and B/X starting with the Eldritch Wizardry supplement in ...
A monster's hit points are derived from their hit dice
From the introduction to the Monster Manual on Hit Points (p. 7):
A monster's hit points are presented both as a die expression and as an average number. [...]
A monster's Constitution modifier also affects the number of hit points it has. Its Constitution modifier is multiplied by the number of ...
They should be safely expelled.
When a creature is polymorphed, it gains the stat block of the form it was polymorphed into, as is stated by the Polymorph spell:
The target's game Statistics, including mental Ability Scores, are replaced by the Statistics of the chosen beast.
As a result, it loses the special ability that allows it to swallow a ...
It isn't quite so easy given that AC calculations have changed between editions as well as underlying philosophies (eg. there are no +5 weapons in the core 5th edition rules and no +5 armor either).
AD&D AC more or less worked like this though, an AC of 10 equated to you having no armor on at all (DEX was not applied in that edition). An AC of 0 equated ...
Conversion document suggests using the HD
There is no direct one-to-one correspondence due to the "bounded accuracy" design principle of 5e. Instead of converting the THAC0, the simplest thing to do, would be to use the following method from the Conversion to the 5th Edition D&D document published by the WotC:
Attack roll modifiers are HD/2 + 2, up ...
Option #1 is correct
The slaad makes three attacks a round. The multiattack ability is not limited to the slaad form, only which attacks it can select as part of that ability.
The slaad can only make one bite attack as part of the multiattack. This is not possible while in humanoid form so the first of the three possible attacks is foregone.
It can also ...
Attacks from any creature other than beast or humanoid are considered magical:
so aberration, monstrosity, dragon, etc. all count as magical for overcoming magic resistance.
In additional humanoid subtype of shapechanger is considered to have magical attack when using its natural attacks. So a werewolf using a longsword couldn't damage another ...
No object or item but there is a person
That person is the DM.
It’s good to be the Dungeon Master! Not only do you get to tell fantastic stories about heroes, villains, monsters, and magic, but you also get to create a world in which those stories live.
Dungeon Master’s Guide p.4
This sounds like a really fantastic story. So tell it. Create whatever ...
Perhaps this could be done with a Wish spell, or a series of Wishes cast day after day by a group of wizards responsible for imprisoning the town.
Another idea is a modified "deck of many things" with an over-abundance of Fate cards:
"The Fates: Reality's fabric unravels and spins anew, allowing you to avoid or erase one event as if it never happened. You ...
The Yochlol's Shapechanger ability states that:
Its statistics are the same in each form.
Meaning that it keeps the stat block of the Yochlol and doesn't gain the statistics of the form it changes into so it is unaffected by a typical Drow's sunlight sensitivity.
No, disadvantage on ability checks doesn't affect the fixed DC
If a vampire makes an unarmed strike attack and the attack is successful, it can choose to grapple instead of dealing damage. (MM, p. 297) Interestingly, the DC is already set as with other monster grapple attacks. The Vampire does not make a Strength (Athletics) check as is described in the ...
Look into the spell Know the Enemy.
There's nothing inherent in the knowledge skills that allows you to have a better bonus at identifying creatures over other things that overlap that knowledge area, but this spell grants a +10 bonus to knowledge checks for the purposes of identifying a creature only, so that seems like something you'll want to look in to, ...