If Witch Bolt initially hits a target that has cast Mirror Image, does the ongoing damage hit the actual target automatically?

Question

In my campaign, a character used witch bolt against an illusionist and hit, dealing 12 damage. The illusionist proceeded to cast mirror image.

Witch bolt states:

On a hit, the target takes 1d12 lightning damage, and on each of your turns for the duration, you can use your action to deal 1d12 lightning damage to the target automatically.

While mirror image states:

Each time a creature targets you with an attack during the spell's duration, roll a d20 to determine whether the attack instead targets one of your duplicates.

Assume the initial attack hits the actual target. Does the ongoing damage from witch bolt (after the initial hit) automatically hit the target, or does a roll occur to determine if it hits the right one?

Answer 1

The ongoing damages aren't attacks, and are unaffected by mirror image

Quoting the text of mirror image with emphasis:

Each time a creature targets you with an attack during the spell's duration, [...]

"Attack" has a specific definition (see this answer for more detail); it's only an attack if it requires an attack roll. Once the initial attack hits, subsequent applications of damage no longer require an attack roll, therefore they're not attacks as far as the rules are concerned. Since Mirror Image only works on attacks, it is ignored.

Answer 2

No

From the description of Witch Bolt, it's clear that the ongoing damage is applied to the same target as the original damage.

From the description of Mirror Image, it's clear that based on the d20 roll, the target is changed. ("the attack instead targets one of your duplicates").

If the original target is changed, and the ongoing damage hits the same target, that ongoing damage must also apply to the changed target. If that target is destroyed it'd end the spell just as if the initial blast from Witch Bolt killed the target.

Answer 3

Based on the wording of the spells, the correct target who was hit by Witch Bolt is unofficially "Statused" if you will. (Wrong term, right idea.) Witch Bolt's extra damage is tied to the specific creature it hit and will continue afflicting him despite the Mirror Images. Of course, if you meet any of the conditions for Witch Bolt's damage to end, (not spending your action to deal the extra damage, being out of Witch Bolt's range, or having total cover from the caster,) Witch Bolt would then stop working. Effectively, the extra damage is like feeling the after shocks of being struck by lightning. The duplicates will also act like they are in pain, however, since they mimic the original and thus will not give away the original's identity as a result.

Answer 4

The original scenario states that the target casts mirror image AFTER which bolt. In this case, mirror image will be ignored, as the which bolt is already linked to the target. Now: it mirror image was cast before which bolt, then there is a reasonable chance that which bolt will fail: if it hits one of the illusions, that illusion will immediately “die” and hence the spell is done, it can’t be transferred to a new target.