Illusory Substitute

By taking control of what those around you see, you make them think a target is not where they actually are using a timely bit of invisibility and an illusion of the target.

Redirect an ability targeting the target at thin air or another target within 5 ft. instead.

(Ability is the blanket term for just about anything that can be done, be it an attack, spell, or other action).
You may cast this spell after seeing the result of the roll.

This spell momentarily turns the target invisible and replaces them with an illusion of them. Both the invisibility and illusion end when this spell does. You may move the illusion up to 5 ft. from the target, though moving to a different space is not necessary to make the illusion be affected by an ability instead of the real target. You control this illusion’s appearance and what it does as it dissipates. You may have it act out being struck before vanishing instantaneously, turn into mist, appear to shatter into a million shards of glass, split into a flock of ducks which fly off, or something else.

Limitations:
Area of Effect:
Attacks or abilities which affect an area ignore this spell and still affect the target.

Grab:
While the target is grabbed, this spell will not work.
This spell does not work on creatures grabbed by the target.
(An attempt to grab the target can still be redirected by this spell.)

Shapesense:
If the target is within a creature’s shapesense range, this spell will not work on them.

Secret:
There is no indication that this spell is being cast.

This spell cannot be identified as it is being cast.
Casting this spell cannot be used as a trigger.
This spell taking effect cannot be used as a trigger,
unless you have a way of knowing it has been cast (the most reliable being shapesense or grabbing the caster).

Simply being aware that a subtle illusion spell has been cast threatens to negate its effect, so a critical component of such spells is ensuring nobody knows when they are cast.

Subtle:
Casting this spell while hidden does not cause you to become unhidden.

Suggested Backfire: You summon a hostile doppelganger of yourself.

Interactions:

Counterspell:
This spell cannot be Counterspelled, because recognising that this spell is being cast is impossible.

Dispel:
In theory, this spell can be Dispelled, but dispelling it is fraught with challenges.

As with any flash enchantment, only a readied Dispel can be timed to dispel Illusory Substitute.
In order to even conceive of Dispelling this spell, you must either already know an enemy can use this spell, most likely from seeing them use it in a prior fight, or be using Dispel proactively in a display of caution.
If you have the means to know for certain that this spell has been cast, you probably are unaffected by it, and therefore have no need to dispel it, though an ally without those means may appreciate the help.
If you do not know whether or not this spell will be cast, you will be dispelling blind, and must use a trigger for your readied Dispel other than Illusory Substitute being cast, such as the next time an ally hits, and may waste time and resources trying to Dispel a spell that is never cast.
To make matters worse, the caster will likely see you readying a Dispel, and may use that information to decide not to cast this spell.
Against a skilled opponent, protecting a critical action from being redirected, or using Dispel to delay or deter Illusory Substitute is more likely than negating the spell, but this can occasionally have its uses.
However, if you force an enemy into a situation where they must cast this spell or lose, the ability to Dispel it may be relevant.

If a single target Dispel targets the target of an Illusory Substitute, the Dispel is redirected to the illusory substitute, and because this counts as redirecting an ability, the spell ends (There is no need to roll to Dispel, the spell will immediately end either way). This can allow the ability which Illusory Substitute was trying to redirect to hit its intended target.
If Negation Barrage is redirected, it does not affect any other magical effects on the target.
An area Dispel affecting the target of an Illusory Substitute bypasses being redirected because it is an area of effect spell, and may roll to Dispel any one magical effect on the target, including Illusory Substitute.