What is the weapon attack damage of a tentacle rod?

Question

The tentacle rod's description includes the following (emphasis added):

Made by the drow, this rod is a magic weapon that ends in three rubbery tentacles. While holding the rod, you can use an action to direct each tentacle to attack a creature you can see within 15 feet of you. Each tentacle makes a melee attack roll with a +9 bonus. On a hit, the tentacle deals 1d6 bludgeoning damage.

Answering this recent question, I concluded that the three-attack feature of the tentacle rod is incompatible with extra attacks from its user. In this older question, it was concluded that it is also incompatible with opportunity attacks.

Usually, magic weapons have the respective item category (e.g. the scimitar of speed, which says "weapon (scimitar)") that defines damage based on those weapon types detailed in the PHB (p. 149). The description clearly states that the rod is a weapon (vide infra), its category, however, is rod. Rods, contrary to staffs, cannot usually be used as quarterstaffs (see this question about rod of the pact keeper).

It seems, therefore, that the tentacle rod is a weapon by RAW but has no weapon type or weapon damage defined.

The rules on improvised weapons (PHB pp. 147-148) state:

An improvised weapon includes any weapon you can wield in one or two hands, such as broken glass, a table leg, a wagon wheel, or a dead goblin. Often, 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.

It further states:

An object that bears no resemblance to a weapon deals 1d4 damage (the DM assigns a damage type appropriate to the object).

Now the last part should not apply because the rod clearly is a weapon. I can simply decide what weapon the rod is like (probably a quarterstaff, club, or a whip).

TL;DR

I could not find conclusive information on what the damage would be when making a normal weapon attack with a tentacle rod.

Is there anything more clear on the subject of the amount of damage, either additional rules on improvised weapons, or specific information on the tentacle rod, that would give guidance on the matter?

Answer 1

I can find nothing in the description of magical rods in general, or the tentacle rod in particular, that defines its weapon properties.

... in 5e. It may be worth noting that 3.5e’s description of the physical properties of magic rods said

Many, as noted in their descriptions, can function as light maces or clubs due to their sturdy construction.

This obviously does not apply directly to 5e, and even if it does it still leaves a question of whether the tentacle rod should behave like a club or a light mace, but it does give precedent to the idea that if you wield a magical rod, even if you are not or even cannot activate its magic powers, you can always hit ’em with it. That, to me, speaks to “weapon” being used correctly in the description here, not as very-poorly-chosen descriptor.

I would not, personally, even rule it as an improvised weapon—it says that rods have “sturdy construction” that allows them to “function as light maces or clubs.” I would rule it as a fancy club or light mace. It may not matter, but if for any reason you are better with clubs or light maces than you are with some random improvised weapon, I’d let you have it.

Answer 2

First, its magic item type is:

Rod, rare (requires attunement).

Compared to say:

Vorpal Sword

Weapon (any sword that deals slashing damage), legendary (requires attunement)

I believe in this case the word weapon is being used only as a descriptor and not as an identifier of a weapon (capable of use in anything that affects weapons.) This actually happens occasionally, even in the same section of the DMG. Such as under the description of

Dragon Scale Armor

While wearing this armor, you gain a +1 bonus to AC, you have advantage on saving throws against the Frightful Presence and breath weapons of dragons, and you have resistance to one damage type that is determined by the kind of dragon that provided the scales (see the table).

Breath weapon describes a dragon (and dragonborn's) breath ability. However even though it uses the word "weapon" it does not make it eligible for say, extra attack, or spells which affect weapons.

Also consider the DMG has a rule stating all magic staffs can be treated as quarterstaffs. However no such rule appears for rods.

As such RAW the Tentacle Rod would only be able to be used as an improvised weapon. As such it is 100% in the DM's judgement as to allow it to be treated as an existing weapon. Logically a whip, flail or club could make sense. But until the DM OKs that, it is only the 1d4 bludgeoning improvised weapon when used in an attack (such as Attack of Opportunity)

Conclusion: It's completely up to the DM. (although several weapons could make sense)

Answer 3

So, from what I can gather: The rod is a weapon as the tentacles are things that make melee weapon attacks. I'd personally allow a 1d6 improvised melee weapon attack with finesse, likening it to a whip, but respecting the rod's innate damage. Maybe reduce the range to 10 feet from 15 for the improv, and let it be magical for the sake of overcoming resistances.

The Rod itself is a Rod. Looking at other items in this category, their many purpose seems to be caster supplements (not that casters need further supplementing in 5e), caster replacements, or a utility item. The only other one I can find with explicit weapon attacks other than this one is the Rod of Lordly Might, which says in its description it functions as a +3 mace for attacks made with it.