Another question brought up a scenario where a crimson assassin used the supernatural ability prayer attack to deliver a coup-de-grace to a PC. The question was about how to prevent the coup-de-grace.
Prayer attack specifically notes that it requires concentration, but there are no rules that I can find for concentration checks on a supernatural ability. If it requires a concentration check, a fascinated creature's allies can save him by dealing damage to the assassin. This seems like a clear design reason to require a check. Do the rules support this interpretation?
Prayer attack
At 2nd level, a Crimson assassin learns her signature assassination style. To initiate a prayer attack, she holds her sawtooth sabre (or sabres) out, point down, and weaves the blade in the air. She must be within 30 feet of and visible to her victim. Beginning a prayer attack is a standard action, and causes her victim to be fascinated by her unless he makes a Will save (DC 10 + the Crimson assassin’s class level + her Charisma modifier—if she’s wielding two sawtooth sabres, this DC gains a +2 bonus). She can maintain the fascination effect by concentrating. The victim may attempt a new save to escape fascination each time a threat (other than the fascinating assassin) appears. At any point after 3 rounds, she may make a coup de grace attack against the target, provided the target is still fascinated. Activating or concentrating on maintaining a prayer attack does not provoke an attack of opportunity.
Can this concentration be interrupted by taking damage? It seems like it would be hard to concentrate while getting smashed in the face, but the rules don't seem to cover this.
The rules for concentration checks specifically talk about "casting a spell." There are rules for losing concentration on a spell due to damage while casting, but this is not a spell.
There are three definitions of supernatural ability.
From the magic page:
Supernatural Abilities (Su)
These can’t be disrupted in combat and generally don’t provoke attacks of opportunity. They aren’t subject to spell resistance, counterspells, or dispel magic, and don’t function in antimagic areas.
From the special abilities page:
Supernatural Abilities (Su)
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.
From the combat page:
Supernatural Abilities (Su)
Using a supernatural ability is usually a standard action (unless defined otherwise by the ability’s description). Its use cannot be disrupted, does not require concentration, and does not provoke attacks of opportunity.
These are general rules, and seem to mostly be a general description. Specific rules overrule general rules, and this supernatural ability specifically requires concentration. RAW, Does this mean it "can be disrupted in combat?"
Best Answer
So there are two different issues to concentrating:
Concentration can usually be disrupted.
Concentration takes your attention, read, your action.
Concentrating on a magical effect is a standard action. While you are concentrating, you cannot be doing other standard actions (usually).
So as a supernatural ability, the prayer attack cannot be disrupted. You do not need to make Concentration checks (or, equivalent, you automatically pass them, since it’s impossible to be disrupted). But you still do have to pay attention to what you’re doing. So you have to spend standard actions each round concentrating on the effect to keep it going.
In effect, the prayer attack has a duration of “Concentration” which is distinct from the idea of concentrating on something to avoid disruption.