Vampiric Touch while mounted on FS/FGS. What melee spell attack does my steed use?

Question

Vampiric Touch is a Self spell. During this spell, you have the option to

Make a melee spell attack against a creature within your reach.

Find Steed/Find Greater Steed

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

Do I take my mount's highest mental stat plus its proficiency bonus to calculate its spell attack modifier, or since it's one spell, does it use my (the caster's) modifier?

Relevant Rules Text;

PHB, Page 202; Rules of Magic -> Range: "Other spells, such as the shield spell, affect only you. These spells have a range of self."

PHB, Page 204; Rules of Magic -> Targets: "A typical spell requires you to pick one or more targets to be affected by the spell’s magic."

Vampiric Touch; Range -> Self

Valid Targets: Self.

Conclusion; the attack roll is a feature granted by the spell cast on yourself, with its own separate targeting function, much like the natural weapons function of Alter Self.

Alternate conclusion; Vampiric Touch (and Alter Self; natural weapons) does nothing, because creatures other than self are not a valid target for any component of the spell.

Answer 1

A direct reading of the rules does not allow Vampiric Touch to affect the mount provided by Find Steed.

The requirement of Find Steed is that the spell targets only the caster:

While mounted on your steed, you can make any spell you cast that targets only you also target your steed.

The text of Vampiric Touch specifies that there may be targets other than the caster (emphasis mine):

On a hit, the target takes 3d6 necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt.

Hence, such spell does not fulfill the main requirement for having the mount affected by the spell.

Moreover, recall that the "range" entry in the spells description does not correspond to the target(s) of the spell.

A DM can rule otherwise.

There is still a debate about what is a target for a spell, since the rules are not completely consistent. See for example the rules for Range:

The target of a spell must be within the spell’s range. For a spell like magic missile, the target is a creature. For a spell like fireball, the target is the point in space where the ball of fire erupts.

and the description of Fireball (see the discussion in this answer about this topic).

For spells with range of Self, the rules say (emphasis mine):

Most spells have ranges expressed in feet. Some spells can target only a creature (including you) that you touch. Other spells, such as the shield spell, affect only you. These spells have a range of self.

Under this description, it seems the spell with range of self effectively target the caster. But Vampiric Touch specifies (emphasis mine):

Make a melee spell attack against a creature within your reach. On a hit, the target takes 3d6 necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt.

A loose interpretation of the description may suggest that the actual target of the spell is the caster, while "target" in spell's text refers to the target of the particular attacks granted by the spell and not to the spell's target.

The next section covers this last interpretation.

Under the magic items rules, only the proficiency bonus of the mount applies for its attacks.

If the DM allows Vampiric Touch to affect also the mount, the bonus for the attacks is given by just the proficiency bonus of the mount, since it has not any spellcasting ability. This can be inferred by the rules for Magic Items in the DMG, page 141:

If you don't have a spellcasting ability-perhaps you're a rogue with the Use Magic Device feature- your spellcasting ability modifier is +0 for the item, and your proficiency bonus does apply.

Indeed, who is making the attack is the mount, not you (the original caster), so it has to use its own abilities. Compare with the Faithful Hound spell, which on the other hand specifies

The hound's attack bonus is equal to your spellcasting ability modifier + your proficiency bonus.

See also the table in the Sage Advice Compendium about How do I know which ability modifier to use with an attack roll and its damage roll? .

Answer 2

Vampiric Touch cannot be shared with your steed

Vampiric Touch has a range of Self, but the target also includes the creature you're touching, not just you:

Make a melee spell attack against a creature within your reach. On a hit, the target takes 3d6 necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt.

As your own quote mentions, the spell must target only you to be shared; since Vampiric Touch does not target only you, so it's not eligible to be shared with your steed.

As a rule, if the spell, by any means:

1. Grants you a special (typically spell) attack (e.g. Vampiric Touch)
2. Includes an attack (e.g. Booming Blade)
3. Triggers a saving throw targeting anyone else

then it's not a spell targeting "only you", because the spell itself is responsible for that attack or save. Conveniently, this means you never need to worry about the attack roll or save DC the steed should use; if the spell allows for an attack/triggers a save, the steed can't use it.

There's some ambiguity for spells that don't grant an attack, just create a weapon, e.g. Shadow Blade, but barring unusual circumstances, your steed can be safely assumed to be unable to wield a weapon (they don't have hands), so the problem doesn't arise there either. If the situation does arise, it would be because of a spell that provides a weapon to be used with normal attacks, and if the DM rules that such a spell is sharable, the weapon would be used like any other weapon (e.g. a mount would need appropriate appendages to hold it, and would only apply their proficiency bonus if they were proficient with that weapon type, etc.).

Answer 3

Most discussions about this try to use "target" as an unambiguous, technical term; but, the rules don't ever clearly define it as such. So the answer to your question depends on what the proper target of VT is. Is it self because that's what the range is, or does it have a secondary target?

Most likely, the rules and terminology evolved from simpler usage, e.g. Fire Bolt, that 1) don't require concentration, that 2) don't have a range of self, or that 3) create each effect per casting. But, the terminology gets much more ambiguous when you add these complications.

A conservative approach would ignore VT's "range" and rule that the spell targets the attacked creature because of the explicit wording of the spell

"On a hit, the target takes..."

And, this approach is generally accepted for similar spells like Booming Blade or smites. But, including the word "target" in the spell description doesn't solve the problem. Consider, Dragon's Breath, which creates a magical effect with a given duration. Dragon's Breath has a range of "Touch", and makes no mention of the word "target". Does this mean it can be duplicated under FS/FGS rules? Maybe. What about a spell like Misty Step, which has a range of self and NO explicit target? RAW

any spell you cast that targets only you also target[s] the mount

but, RAW do not explicitly state that "you" are the target--only that "you teleport".

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Given the ambiguity, the best option is for a GM to make a ruling; but, convention is to rule that VT cannot be duplicated on a mounted steed through FS/FGS. However, it should really boil down to the distinction between spells that create a lasting effect and ones that create an immediate effect. For example, some spells, like Magic Stone, magically imbue an item, which can be later used to make a spell attack against a target. Is VT more like Magic Stone or more like Fire Bolt? If the former, FS/FGS should work, conversely, the latter should not work.

In my opinion, the best ruling is the one that works best for the people involved. If you can convince your GM to grant you this ruling, you might look to Magic Stone as an example (using the caster's spell casting ability and modifier)