How do the Crag Cat and Chain Lightning spell interact?

Question

The Crag Cat (SKT, p. 240) is a CR 1 creature that has the unique feature of Spell Turning:

The cat has advantage on saving throws against any spell that targets only the cat (not an area). If the cat's saving throw succeeds and the spell is of 7th level or lower, the spell has no effect on the cat and instead targets the caster.

Emphasis mine.

Chain Lightning is a spell that targets a single target initially, but also hits several other targets afterward.

You create a bolt of lightning that arcs toward a target of your choice that you can see within range. Three bolts then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target. A target can be a creature or an object and can be targeted by only one of the bolts.

I am curious how the spell and creature interact:

1. If the cat is the target of a residual bolt - can the residual bolt reflect back toward the caster?
2. If the cat succeeds the initial save - does the spell reflect to the caster and then target several others, which could potentially be the cat again?
3. Who decides where the spell jumps to should the cat successfully reflect the initial bolt - the cat or the caster?
4. Does the cat get another reflecting save should a secondary bolt target it after the initial reflected bolt?

Answer 1

The crag cat's Spell Turning feature will almost never apply to chain lightning

The most literal reading is that the crag cat's Spell Turning ability applies to chain lightning if and only if the cat is the only target chosen. If multiple targets are chosen when the spell is cast, the ability does not apply. However, casting chain lightning on only a single target is quite a wasteful use of the spell and is therefore unlikely to ever occur in practice. (What's the point of chain lightning that doesn't chain?) This means that in almost all cases, the cat's ability will not apply to chain lightning, even though it would technically be possible under specific circumstances.

Note that the distinction between the primary and secondary bolts of lightning is irrelevant here. All targets are chosen simultaneously when the spell is released, and if there are any secondary bolts, then the spell has multiple targets and the cat's ability does not apply. It doesn't matter whether the secondary bolts logically occur after the primary bolt. Mechanically, the targets are chosen simultaneously and the damage occurs simultaneously.

The erratum for Twinned Spell may or may not apply

The sorcerer's Twinned Spell metamagic uses a similar wording to describe which spells it can be used on:

When you cast a spell that targets only one creature...

and this was later clarified in an erratum:

To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level. For example, magic missile and scorching ray aren’t eligible, but ray of frost and chromatic orb are.

If we apply this erratum to the similar wording in the crag cat's Spell Turning ability, then the ability would never apply to chain lightning regardless of how many targets are selected. Simply the ability to select multiple targets would make it ineligible. Unfortunately, the erratum doesn't say whether this clarification applies specifically to twinned spell or generally to any ability with a similar wording. Either ruling would be reasonable for a DM to make. Luckily, as mentioned above, the only time it would matter is when the crag cat is the only target chosen for a chain lightning spell, which is almost never going to happen.

(Thanks to @KamilDrakari for pointing this out.)

Answer 2

RAW, the Crag Cat cannot Spell Turn Chain Lightning

The most straightforward response is that the Crag Cat can't turn Chain Lightning at all. The wording of the spell doesn't suggest the initial target is distinguished, all creatures in the chain are simply targets of the spell.

See Can Twinned Spell affect Chain Lightning?

Nonetheless, I wouldn't be shocked or argumentative if a DM ruled otherwise. Speculation: perhaps this would be based on an intuition that Chain Lightning is somehow an iterative spell, and the first target is the target. Personally, if I was working from that premise, I'd expect the cat to get a save against every "bolt", and for each "bolt" to be reflected at the previous creature in the chain.

Answer 3

The Crag Cat can turn chain lightning

Why it works

The turning ability contains the text:

The cat has advantage on saving throws against any spell that targets only the cat (not an area). If the cat's saving throw succeeds and the spell is of 7th level or lower, the spell has no effect on the cat and instead targets the caster.

I take the "(not an area)" to mean that chain lightning can work with this ability as it is not an area of effect spell but a targeted one.

Your examples

If the cat is the target of a residual bolt - can the residual bolt reflect back toward the caster?

When targeted by a residual bolt the cat is the only target for the spell. This qualifies for spell turning and should reflect back toward the caster.

If the cat succeeds the initial save - does the spell reflect to the caster and then target several others, which could potentially be the cat again?

The initial spell would reflect back toward the caster, there is nothing to say the caster isn't a valid target for the spell. Therefore is could leap onto to other targets. Some DMs may rule you need to pass a concentration check or the spell fails after you take damage and before it leaps to another target.

Whether or not you can target the cat again would vary by DM. I would probably rule that you can't, as "A target can be a creature or an object and can be targeted by only one of the bolts".

Who decides where the spell jumps to should the cat successfully reflect the initial bolt - the cat or the caster?

The caster decides who the spell leaps too. The cat is only reflecting the spell, not controlling it.

Does the cat get another reflecting save should a secondary bolt target it after the initial reflected bolt?

The cat would get a save each time it was targeted by the spell. It's Spell Turning feature also doesn't require an action and can be used on every save so it could also reflect additional bolts. This is another reason why I would rule that you could not target the creature again with the same casting.

Range and targeting

It is important to note that the Crag Cat's ability says "targets the caster" not "caster takes the damage" this means that the spell has no effect if the caster is not a valid target.

For chain lightning it has an initial range of 150ft. If the Crag Cat is targeted directly they can turn the spell back as the caster must be within this range to target them.

For each additional bolt however the range is 30ft from the initial target. If the caster is not within 30ft of the initial then the Crag Cat's ability will cause the spell to have no affect on it, but not target the caster as they are not a valid target.