What happens when the wearer of a Shield of Missile Attraction is behind total cover?

Question

The Shield of Missile Attraction, a rare magic item that requires attunement, has the following curse:

Whenever a ranged weapon attack is made against a target within 10 feet of you, the curse causes you to become the target instead.

Say there are two creatures, one (let’s call it A) in clear arrow path and the other (let’s call it B) within 10 feet of A but behind total cover (such as a wall) but also cursed by a Shield of Missile Attraction. What would happen if someone tries to make a ranged weapon attack (such as shooting an arrow) at A?

1. As there is not a clear arrow path to B, the shield's Missile Attraction property does not work and A gets shot.
2. B becomes the target, but the Missile Attraction’s arrow deviation also causes the arrow to somehow go around the wall and B gets shot.
3. B becomes the target, but the wall takes the arrow so that neither A or B gets shot.
4. Some other scenario I haven't envisioned.

Answer 1

RAW, B is targeted

One of the foundational rules for playing the game (found in the Introduction to the Basic Rules):

many racial traits, class features, spells, magic items, monster abilities, and other game elements break the general rules in some way, creating an exception to how the rest of the game works. Remember this: If a specific rule contradicts a general rule, the specific rule wins.

In this case we have the specific rule from the magic item shield of missle snaring contradicting the general cover rules:

A target with total cover can't be targeted directly by an attack or a spell

Regardless of the cover, the specific rule of the shield trumps any targeting limitations as the shield says (emphasis mine):

Whenever a ranged weapon attack is made against a target within 10 feet of you, the curse causes you to become the target instead.

Whether or not you are a valid target at the time of the attack is irrelevant as the specific magic item rule makes you into the target. No exception is provided by the specific rule (for what it's worth, it specifies "whenever").

How to narrate this

Total cover states that you can't be targeted directly by an attack. Perhaps the shield magically modifies the trajectory to take a path to you (similar to how fireball's effect can go around corners). If you are behind total cover, the arrow navigates around the cover.

A GM could then rule that your position relative to the new indirect trajectory has half cover, three quarters cover, or even impose disadvantage as he/she warrants. This is part of the procedure for Making an Attack:

Determine modifiers. The GM determines whether the target has cover and whether you have advantage or disadvantage against the target.

There is also an optional rule in the Dungeon Master's Guide called Hitting Cover that could aid in the narration:

When a ranged attack misses a target that has cover, you can use this optional rule to determine whether the cover was struck by the attack.

Essentially if the attack would have hit the target without the three-quarters cover (or whichever you impose) but the +5 AC makes it a miss, the cover blocks the arrow.

Rules as Common Sense

As a general disclaimer, a GM can rule that the cover provides substantial AC to block the arrow as a common sense ruling. Any GM can change the rules so the table can enjoy the game to their highest degree.

Answer 2

RAW - the curse should work. It's magic!

Going purely by RAW, the words are clear in that the curse causes the attack to target the cursed. No matter what. As quoted above, there is no case stated where it won't. It just does.

The magic of the curse extends beyond all the rules on targeting, other effects, range, etc. and as long as they are within 10' of the original target, they'll become the new target of the attack.

Bringing in other rules regarding, targeting, cover, etc. aren't necessary as the specific language of the curse overrides those general everyday rules and requirements.

But the RAW ruling has flaws and I'd like to suggest a more reasonable one

RAW creates a lot of other interaction issues that don't make sense

Let's say that Target B is actually inside, but at the edge Leomund's Tiny Hut and Target A is standing just outside of the Tiny Hut within 10' of them.

If we allow the curse to work as planned, then it would also bypass the specific rule of the hut preventing objects moving through it and that does not seem like the likely interaction.

Nor does it seem likely that 3/4 cover should be more beneficial than total cover as there is no penalty besides not a valid target for total cover.

Ruling the curse to work this way creates more issues than it solves and it's best to keep it simple rather than generate a slew of unintended consequences by allowing it.

Suggested ruling

The core question here is what happens to a ranged weapon attack that has an invalid target. The total cover rules state:

A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect.

So what's happening is The arrow initially targets creature A, but the curse wants to attract the missile, but it can't because creature B is not a valid target. By being an invalid target, the curse cannot come into effect.

Narrative common sense

I do agree that it seems like the Shield should draw the arrow to the wall and have it miss creature A. There is an optional rule for Hitting Cover that could present a case allowing this.

When a ranged attack misses a target that has cover, you can use this optional rule to determine whether the cover was struck by the attack.

First, determine whether the attack roll would have hit the protected target without the cover. If the attack roll falls within a range low enough to miss the target but high enough to strike the target if there had been no cover, the object used for cover is struck.

However, the problem here again is that Creature B is not a valid target, but if a DM wanted to rule that it draws the missile anyway and it hits the wall, I'd be okay with that. Rules as fun!