Can a Mounted Combatant force enemies to make spell/ranged attacks on it?

Question

My question concerns the Mounted Combatant feat, specifically the clause which states:

You can force an attack targeted at your mount to target you instead. (PHB p. 168)

I just started DMing a new campaign in which one of my players is using a homebrew archetype Dragon Conclave Ranger with a Lesser Dragon mount and has the Mounted Combatant feat. His dragon mount is a large creature.

He thinks that the use of this feat means that he can force any attack to target him instead of his mount, including ranged weapon attacks and all spell attacks (melee + ranged), not just the Attack action. I think this would be a little overpowered. It also does not seem to make much sense that the mountee can draw away an attack from the mount if for example the enemy is a sharpshooter with excellent aim specifically aiming a bow/x-bow at a dragon which is larger than the mountee himself, or a wizard aiming a magic missile at the dragon. However, the language is kind of vague, so I'd like to get someone's opinion on the matter. My inclination as a DM would be only to allow melee attacks, but since ranged weapon attacks also count as part of the Attack action I can see that being acceptable under RAW as well.

Any insights would be much appreciated. Thank you.

Answer 1

Your player can redirect ranged and spell attacks.

PHB 193 is clear that "attack" encompasses melee, ranged, and spell attacks:

Whether you’re striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.

PHB 194 goes on to specify that an "attack" involves an attack roll:

When you make an attack, your attack roll determines whether the attack hits or misses. To make an attack roll, roll a d20 and add the appropriate modifiers.

The text of the feat, as you quote, simply says "attack". It doesn't make any exceptions based on the size of the mount.

However, spells that don't require attack rolls, such as Magic Missile or spells that require saves, are not "attacks" for this purpose.

Additionally, the MM is full of examples of large, dragon-like creatures specifically called out as mounts. For instance, the Wyvern (CR 6) can be used as a mount (MM 303):

A wyvern can be tamed for use as a mount, but doing so presents a difficult and deadly challenge.