What spell level should this homebrew After-Image spell be?

Question

I came up with a cool spell idea, but I'm unsure of what level it should be. Here's the spell:

After-Image

4th-level conjuration

Casting Time: 1 reaction, which you take when you would be hit by an attack

Range: Self

Components: V, S

Duration: Instantaneous

When you are the target of an attack roll that would hit you, this spell allows you to instead appear 5 feet away from where you were initially standing, causing the attack to pass through your after-image and deal no damage to you. This spell can only protect you from one attack, and cannot affect critical hits.

If you would need to move more than 5 feet to avoid the attack, you move the minimum distance needed to avoid the attack.

I would imagine that 4th level is high enough, but since this is a guaranteed dodge of one attack at the cost of your reaction, I'm not entirely sure. Can anyone produce a similar spell that suggests a level for this spell, or a good argument for a certain level for this spell?

Answer 1

Making it 5th level closely replicates the power level of an existing class feature

At 10th level (character level, not spell level), wizards of the School of Illusion get the Illusory Self ability, which is nearly identical to your spell:

Beginning at 10th level, you can create an illusory duplicate of yourself as an instant, almost instinctual reaction to danger. When a creature makes an attack roll against you, you can use your reaction to interpose the illusory duplicate between the attacker and yourself. The attack automatically misses you, then the illusion dissipates.

Once you use this feature, you can’t use it again until you finish a short or long rest.

They can do this at most once per battle, and on average 3 times a day (assuming the "standard" adventuring day with 2 short rests). If you want to put your spell on a roughly equal power level to the very similar Illusory Self feature, make it a 5th level spell. This allows a 10th-level spellcaster to use it twice a day (plus a third use for a wizard, using Arcane Recovery). Making it a spell rather than a limited-use class feature means that a character will gain more potential uses of it as they level up and gain more higher level slots. However, this shouldn't be a major problem in practice, since using higher level slots on this spell will feel like a waste to most players, considering the other uses those slots can be put towards.

If you create this spell, you should be aware that you are "stepping on the toes" of the Illusion wizard. Class features are meant to give an unique flavor to the class, and they can feel a lot less special when they can easily be duplicated by a spell, especially if the spell was available first. Of course, this is only an issue if you have an Illusion wizard in your campaign, or might possibly have one in the future.

Teleporting even a small distance is a minor additional benefit

Note that the Illusory Self ability doesn't allow the wizard to move. It just forces the attack to miss. Adding in the very short range teleport has important implications, because it takes the caster safely out of the attacker's melee range. If the attacker used all their movement to reach the caster, then the caster can run away without disengaging on their next turn. Furthermore, if the attacker has no more movement and the caster uses this on the first attack, any additional attacks the attacker could have made are wasted, or must be redirected against other targets instead. This makes your spell a bit more powerful than the Illusory Self feature. This extra power may be justified by the need to use a high level spell slot, which has an opportunity cost, unlike the class feature, whose only opportunity cost is the character's reaction for the turn.

Answer 2

4th-level is, in my opinion, pretty adequate, assuming you get rid of the teleportation.

As Ryan Thompson states in his answer, the 10th-level illusion wizard's feature is ideal for comparison with your spell.

However, there are numerous other features that let you impose disadvantage on an attack roll, increase your AC, or reduce the attacker's roll.

For example:

• Shield, 1st-level spell: +5 to AC, not only against one attack, but against all attacks until the start of your next turn.
• 3rd level Lore Bard's Cutting words: subtract 1 inspiration die from one attack roll
• 3rd level Valor Bard's Combat Inspiration: add inspiration die to AC for one attack roll against you
• 1st-level Light Cleric's Warding Flare: impose disadvantage on one attack roll against you
• Protection Fighting Style: impose disadvantage on an attack roll against a creature (not you) within 5 feet of you
• Battle Master's Parry: reduce roll by superiority die + DEX
• 5th-level Rogue's Uncanny Dodge: reduce damage by half if hit
• 6th-level Wild Magic Sorcerer's Bend Luck: subtract 1d4 from attack roll (the feature can do other things as well, though)
• 6th-level Archfey Warlock's Misty Escape: teleport & invisible after you take damage
• 6th-level Great Old One Warlock's Entropic Ward: impose disadvantage on one attack, and if it misses, your next attack has advantage
• 6th-level Enchantment Wizard's Instinctive Charm: redirects! an attack, so that the attacker might even hit his colleagues
• Defensive Duelist feat: add prof bonus to AC against 1 attack

Clearly, a 100% guaranteed miss is stronger than imposing disadvantage or subtracting a number from the attack roll / adding it to your AC.

However, many of these features (most of them, actually) are available waaay earlier than 4th level spell slots. Furthermore, class features are rarely as strong as the highest level spells available on that level - for instance, take the Shield spell, which increases your AC by 5, and is a 1st level spell. Bards can only do this by level 3, and even at level 5 their average Cutting Words reduction is only 4.5 (5.5 at level 10).
Therefore, concluding from a similar class level 10 class feature that the spell would have to be 5th level is not a valid conclusion.

I believe that, for a guaranteed miss, 4th level is definitely adequate. For comparison, a 4th-level Cure Wounds will heal you by 4d8 + spellcasting modifier, which is more than most enemies deal in a single attack (at least at the level where you gain 4th-level slots).
However, Ryan Thompson is correct in stating that the 5 feet teleportation can be pretty strong - situationally, though; in many cases, the enemy will have movement left. If you keep the teleportation, 5th-level might be adequate, although personally, I would probably never use this spell if it were 5th-level, and even if it's 4th-level, I wouldn't use it until I'm higher level and have 5th or even 6th level slots already. Otherwise, there are numerous better things to do with a level 4 slot - something that's not the case with class features.