Are the Soulmonger's Tentacles considered objects or creatures?

Question

One of the last encounters in the Tomb of Annihilation adventure is against the Soulmonger, an huge, evil artifact:

The Soulmonger is an upright crystal cylinder 20 feet high and 10 feet in diameter. [...]

The Soulmonger is an artifact of evil - a Huge object with AC 15; 200 hit points; vulnerability to radiant damage; and immunity to bludgeoning, piercing, and slashing damage from nonmagical attacks.

The artifact possesses four tentacles, which can throw characters into the lava pit below it:

Once per turn, in response to any creature making a successful melee weapon attack against the cylinder or one of its struts, the Soulmonger attacks that creature with one of its 30-foot-long tentacles. The tentacle bas a Strength score of 22 and makes one melee weapon attack against the creature: +7 to hit, 24 (4d8 + 6) bludgeoning damage. Instead of dealing damage, a tentacle can grapple its target (escape DC 16). If the target weighs 330 pounds or less, the tentacle can also lift the grappled creature and move it to any unoccupied space within its 30-foot reach, or drop it in the lava.

The tentacles can be attacked and destroyed. Each one is a Huge animated object with AC 15, 30 hit points, and immunity to poison and psychic damage.

Each of the tentacles is an "animated object", but I'm unsure what that means exactly. For rule purposes, it is unclear to me whether the tentacles should be considered creatures or objects, or both.

This distinction matters a lot for spellcasting: a large portion of spells only affect creatures, not objects.

Answer 1

They're not objects

The rule says (from here):

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

These tentacles are not inanimate, so they're not objects.

There is no definition of "creature" in the rules

See our discussion here:

It's important to note that "creature" does not get a precise definition in the rules.

(The answer goes on to attempt to define what "creature" means by looking at how it's used in the rules. But that's not a game definition. A post on a Q&A site cannot issue new rules, especially not for something as far-reaching as defining a fundamental term.)

You should treat them as creatures

Spells such as eldritch blast target "creatures". If you decide that these things aren't creatures, then you're deciding that they're immune to a wide variety of damage spells, based on an obscure technicality, and your players will be mad at you.

Describing the tentacles as "animated objects" is probably a reference to the spell

The spell animate objects says:

Each target animates and becomes a creature under your control until the spell ends or until reduced to 0 Hit Points.

which would make them creatures.

Answer 2

They would be considered creatures, not objects

Per the DMG:

For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

Looking at a piece of the description for the tentacle, it states:

Once per turn, in response to any creature making a successful melee weapon attack against the cylinder or one of its struts, the Soulmonger attacks that creature with one of its 30-foot-long tentacles. The tentacle has a Strength score of 22 and makes one melee weapon attack against the creature

And that's important! Why? Because a subheading talks about the stats of objects.

When time is a factor, you can assign an Armor Class and hit points to a destructible object. You can also give it immunities, resistances, and vulnerabilities to specific types of damage.

But the description for the tentacle mentions a Strength score. With few, perhaps only one exception that is something not found on an object.

As pointed out in Dan's answer, there is no definition of "creature" in the rules. It appears everywhere in the book but never given a clear definition. In which case we go with a standard English language definition:

1. an animal, especially a nonhuman
2. person; human being
3. anything created, whether animate or inanimate

This feeds into the later text describing the tentacles as "animated objects". It is both part of the definition and possibly a reference to the animate objects spell.

Each target animates and becomes a creature under your control until the spell ends or until reduced to 0 Hit Points.

The real problem in all of this

As I mentioned as a comment in the other answer, the problem doesn't stem from "what is an object vs what is a creature?" It is with the spells and features that keep saying "target a creature" when the effect is perfectly valid against most objects.

Why wouldn't an eldritch blast, which uses force damage, work on a door or a wall AS WELL AS a goblin and a lich?

As a DM, I generally let any spell work on creatures and objects, so long as it makes sense. You can't revivify a broken door to make it new again. You can't healing word the trap to reset it. You can't speak with plants once it's been made into furniture. You get the idea.

All signs point to them being creatures

So blast away.

Answer 3

It's unclear, but the tentacles are probably objects

It's unclear if the tentacles are creatures or objects. However, if we look at all the available evidence, we can conclude that they are most likely objects.

1. The tentacles are described as "animated objects".

The rule does say that objects are not animated:

For the purpose of these rules, an object is a discrete, inanimate item

There are two ways to interpret the term "animated object": either it is an object that became a creature (similar to the Animate Objects spell), or it is an object that has the unusual property of being animated.

If the animated tentacle is still an object, then this would be an example of a specific rule (the tentacle is both animated and an object") beating a more general one ("objects are not animated").

I could see it go either way. I'll add that there are already multiple examples of objects that are not inanimate, such as a Rock Gnome's Clockwork Toy, a Dancing Sword magic item, or the hand created by the Bigby's Hand spell.

2. The tentacles do not have complete statistics

According to the monster manual (page 8),

Every monster has six ability scores (Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma) and corresponding modifiers.

The tentacles only have AC, HP, Strength, Size, and Damage Immunities. They do not have Dexterity, Constitution, Intelligence, Wisdom, and Charisma scores. This strongly suggests that they are not creatures.

All objects have AC, HP, Size, and Damage Immunities (DMG p.246). Unusually, the tentacles do have a Strength score, but so does the Hand object created by Bigby's Hand.

3. The tentacles do not have a creature type.

According to Jeremy Crawford,

A creature has one of the types listed in the Monster Manual (p. 6–7). A sentient magic item has none of those types. It's an object.

Tomb of Annihilation does not give the tentacles one of the fourteen types: aberration, beast, celestial, construct, dragon, elemental, fey, fiend, giant, humanoid, monstrosity, ooze, plant, or undead.

From Jeremy's tweet, we could conclude that the tentacles are therefore not creatures, but objects.

We could presume that the tentacles are constructs; however this is not at all listed in the book. I think this would be incorrect, just like it would be incorrect to presume that sentient magic items are constructs.

4. The tentacles are not referred as magical in any way

Some argue that the tentacles are animated by magic, in a way similar to the spell Animate Objects. However, there are no reference to the tentacles being in any way magical. They can't be rendered inert through a Dispel Magic or Antimagic Field. This suggests that the animation are mechanical and not magical, and the tentacles move through elaborate mechanical engineering.

5. The tentacles are controlled by the Soulmonger, an object

The tentacles are controlled by the Soulmonger, itself explicitly an object. Presumably, the tentacles are an extension of the Soulmonger. It would make sense for the tentacles to also be objects.

6. The tentacles are not referred as Constructs

If the tentacles were indeed creatures, it would have been so much clearer to describe them as constructs. It would have avoided a lot of ambiguity, and automatically made it clear that they are creatures. The fact that the book uses the nonstandard term "animated object", to me indicates that the tentacles were intended to be objects.

Answer 4

They're objects. The section on them has a final paragraph that says, "The tentacles can be attacked and destroyed. Each one is a Huge animated object with AC 15, 30 hit points, and immunity to poison and psychic damage."

Answer 5

Who cares?

The rules which make it matter are mostly things like 'can I target it with an eldritch blast', and while RAW you might come up with 'no', that makes no real sense.

I haven't found any rules where the creature vs object distinction is useful. Just let abilities, attacks, powers etc affect things that they make sense to affect.

If for example you told my warlock that I can't attack a door with eldritch blast, I would leave your table.