Can any of the found greater steeds benefit from the weapon proficiencies granted by Tenser's Transformation?

Question

The mount summoned by the 4th level Paladin spell find greater steed has this interesting ability:

While mounted on it, you can make any spell you cast that targets only you also target the mount.

The 6th level wizard spell Tenser’s tranformation grants weapon proficiencies;

You have proficiency with all armor, shields, simple weapons, and martial weapons.

After casting Tenser’s transformation while riding my found greater steed, technically my mount would have proficiency with all simple and martial weapons.

Obviously the primary issue here is going to be the question of “appropriate anatomy” - can magic that makes the uncoordinated wizard with no weapon skills a martial juggernaut also give my griffon the basic ability to firmly grasp a short sword? Are any of the mounts listed¹ able to make use of any of the weapon proficiencies granted by Tenser’s transformation?

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¹ a griffon, a pegasus, a peryton, a dire wolf, a rhinoceros, or a saber-toothed tiger.

Answer 1

Short answer is no.

Detailed answer is as follows:

Weapon proficiency in fifth edition of Dungeons and Dragons doesn't define your ability to wield weapons. It defines your ability to wield them effectively - i.e. in game terms - whether you add your proficiency bonus to attack rolls. (PHB, p. 146).

But to use weapons you need obvious "appropriate anatomy", which mounts lack and, probably, a certain level of intelligence.

Tenser's Transformation (XGtE, p. 168) gives the benefits of:

• You gain 50 temporary hit points. If any of these remain when the spell ends, they are lost.
• You have advantage on attack rolls that you make with simple and martial weapons.
• When you hit a target with a weapon attack, that target takes an extra 2d12 force damage.
• You have proficiency with all armor, shields, simple weapons, and martial weapons.
• You have proficiency in Strength and Constitution saving throws.
• You can attack twice, instead of once, when you take the Attack action on your turn. You ignore this benefit if you already have a feature, like Extra Attack, that gives you extra attacks.

It doesn't change caster, nor it override weapon and armor qualities tied to anatomy. I.e. a Small caster under Tenser's transformation would still have disadvantage using heavy weapons (which would cancel the advantage given by the spell). And a wizard with a Strength score of less than 15 would be slowed by plate armor. And an obvious requirement to be able to use weapons would be 'at least one appendage capable of fine manipulation with objects'.

So, if playing by the rules - no, you can't give your mount an ability to have some extra weapons.

Answer 2

No. Unfortunately I've looked everywhere and haven't been able to find a way in the rules to allow those animals with no hands to wield weapons .. barring a friendly DM.

But You can True Polymorph it into a creature that can. Centaurs for example are CR 2 just like the other available mounts. And they can wield weapons.

Answer 3

Can magic that makes the uncoordinated wizard with no weapon skills a martial juggernaut also give my griffon the basic ability to firmly grasp a short sword?

No. Imparting proficiency does not impart appropriate anatomy or physical ability. This can be inferred from magic (for example Polymorph and True Polymorph) that transforms a character's shape while they retain the same weapon proficiencies that Tenser's Transformation would otherwise impart. Just having the proficiency does not grant the ability to use it in the new form. Or, even more explicitly, a druid's wild shape, which says

You also retain all of your skill and saving throw Proficiencies, in addition to gaining those of the creature...You can't cast Spells, and your ability to speak or take any action that requires hands is limited to the capabilities of your beast form. (PHB67)

If someone who already has a weapon proficiency cannot use it in beast form, granting the proficiency to a beast will not give them the ability to use it either. However, the quote leaves open the possibility that some beast forms do indeed have the inherent capability to use these.

Are any of the mounts listed able to make use of any of the weapon proficiencies granted by Tenser’s transformation?

Possibly. Nothing specifically prohibits it, so this is a DM decision. Let us examine to what extent form restricts or allows weapons use.

A monster's type speaks to its fundamental nature...The game includes the following monster types, which have no rules of their own. (MM6)

Since monster type has no rules of its own, there are no rules which state that weapons use is prohibited (or required!) of certain types.

Griffons and Perytons are monstrosities. There are monstrosities that can use weapons (centaurs, doppelgangers) and ones that do not.

Pegasi are celestials. There are celestials that can use weapons (devas, planetars) and ones that do not.

Dire wolves, Rhinoceri, and Saber-toothed tigers are beasts. There are beasts that can use weapons (apes, giant apes) and ones that do not.

On the other hand, while most humanoids use weapons, there are those that do not (quaggoth, troglodytes).

The common denominator among all the different creatures that do use weapons appears to be the possession of hands, as the PHB quote about wild shape emphasizes. Not surprising, since the simple weapons and martial weapons already on the PHB weapons list were designed for animals that have hands. But could there be weapons that do not require the use of hands?

If the DM allowed "spiked hoof boots" as a weapon, I would think it reasonable that proficiency in them would be granted as part of "all martial weapons", and thus profitably gained by greater steed pegasi.

Similarly with "horn blades" on a rhinoceros,

https://lh3.googleusercontent.com/proxy/nsOiNiKz0DAC10noV6SuvU_2F7l8v4pV66rs4hK1Klzk24CEFjxmQPvDuAcAaz0HadO83qB_lLioDgcTr7wXEQ

or "heavy helmet armor proficiency" for a saber-toothed tiger,

https://www.hemanworld.com/wp-content/uploads/2015/04/PCS-Battle-Cat-e1434744585197-620x381.jpg

Finally, griffons and perytons presumably make nests, a process which requires both strength and dexterity in talons and beaks. At the very least, as a DM, I would allow Tenser's Transformation to gain them proficiency in the already-existing weapon of nets, but rather then throwing them, allow them to be dropped from above (for which the peryton's flyby ability would be useful).

Thus, I would argue that since nothing explicitly prohibits steeds from using weapons or armor, Tensor's Transformation would grant proficiency in both already existing weapons and armor which the steed's natural anatomy allowed them to use (as defined by the DM), and even more so for weapons and armor designed to function for their own particular anatomies (as permitted by the DM).

Related: Can a druid in Ape wildshape use weapons?