Does the Arcanist Flame Arc exploit trigger attacks of opportunity?

Question

Does the Arcanist Flame Arc exploit trigger attacks of opportunity?

Here is my gaming group's thought process, to show that we did some research, albeit ultimately came up to nothing and I had to rule on the fly so as to not stop the game for more than the 15 minutes we already spent on the issue. We know that general trumps specifics, so we went:

• Take a read at the Flame Arc exploit

The arcanist can unleash an arc of flame by expending 1 point from her arcane reservoir. This creates a 30-foot line of flame that deals 1d6 points of fire damage + the arcanist’s Charisma modifier, plus an additional 1d6 points of fire damage for every 2 levels beyond 1st (to a maximum of 10d6 at 19th level) to each target in the line. Creatures in the area of effect may attempt a Reflex saving throw to halve the damage.

• Look at the Arcanist Exploit feature

By bending and sometimes even breaking the rules of magic, the arcanist learns to exploit gaps and exceptions in the laws of magic. Some of these exploits allow her to break down various forms of magic, adding their essence to her arcane reservoir. At 1st level and every 2 levels thereafter, the arcanist learns a new arcane exploit selected from the following list. An arcanist exploit cannot be selected more than once. Once an arcanist exploit has been selected, it cannot be changed. Most arcanist exploits require the arcanist to expend points from her arcane reservoir to function. Unless otherwise noted, the saving throw DC for an arcanist exploit is equal to 10 + 1/2 the arcanist’s level + the arcanist’s Charisma modifier.

• The exploit is listed as Supernatural, what does it say there, then?

Supernatural abilities are magical but not spell-like. Supernatural abilities are not subject to spell resistance and do not function in areas where magic is suppressed or negated (such as an antimagic field). A supernatural ability’s effect cannot be dispelled and is not subject to counterspells.

There we went on a grinding halt. I ruled that the player could use it without triggering AoO, but since it acts like a lightning bolt, in my head, I believe it should trigger an attack of opportunity, so I warned him I'd look it up and might change it by the next game and he was quite alright with that decision.

As you have guessed, I am the DM, but also our group's Rule Lawyer and if it says clearly somewhere if the ability triggers or not, I would much appreciate to be pointed in that direction to have a good read.

Answer 1

You were correct: supernatural abilities, flame arc included, do not provoke attacks of opportunity. They also cannot be countered, dispelled, or disrupted. They never require Concentration checks. Basically, antimagic field is just about the only thing that can stop them.

This makes it similar to, say, a dragon’s breath weapon. Those are also supernatural, and often form lines of damage. (None seem to breathe a line of fire, but that’s irrelevant.) Dragons certainly don’t provoke when breathing.

But you claim that flame arc instead “acts like a lightning bolt,” which could not be further from the truth. Flame arc deals 1d6 damage per two levels: lightning bolt deals twice as much (or more, on odd levels). Flame arc does add the arcanist’s Charisma bonus—which may be substantial, but it’s unlikely to make up for very many d6s. That means that a turn spent using flame arc—assuming¹ no resistances or vulnerabilities are in play—does considerably less than a turn spent using lightning bolt. Which very often means it shouldn’t be used at all.

The thing is, Pathfinder combats don’t involve very many turns, and a lot happens in each turn. In the middle of a combat, actions are the most precious resource available—saving a spell slot or what have you doesn’t matter if you’re dead. And flame arc isn’t free—arcane reservoir points are being spent on it. Yes, it’s a bit safer to use than an actual spell, but that’s rarely a major issue since most spellcasters 1. five-foot step out of the way of any threatening creatures, and 2. cast defensively when they cannot.

And finally, it has to be said: lightning bolt is a poor spell. Blasting spells, in general, are pretty poor in Pathfinder. Their damage is difficult to improve, and doesn’t do enough to be worth the hassle. By default, they are worse than attacks, assuming decently-selected feats are improving them. So comparing flame arc against it may not be the best example. It says quite a lot that flame arc doesn’t come out of that comparison looking too hot.

1. _{If we don’t assume we can ignore resistances and vulnerabilities, things only get worse for flame arc as compared to lightning bolt—fire resistances are found on more monsters than electricity resistances, and in most campaigns will be more common.}