Can brimstone blast's bonus fire damage benefit from Mortalbane?

Question

Brimstone blast (Complete Arcane p.132) is intended to be a non-stacking damage effect as opposed to vitriolic blast which just adds more damage every round. However, the wording used to accomplish this is as follows:

A creature burning in this way never takes more than 2d6 points of fire damage in a round, even if it has been hit by more than one brimstone blast.

Does this language prevent brimstone blast's bonus damage from benefiting from the bonus damage from Mortalbane (Book of Vile Darkness p.49)?

Answer 1

RAW:

Sigh. RAW, any creature burning in this way never takes more than 2d6 points of fire damage in a round period. The way English works, if they are burning, they take 2d6 fire damage, and are immune to any other fire damage that round. This would prevent any bonus fire damage from mortalbane as well as additional Brimstone Blasts or any other source of fire damage.

NOT-RAW:

Obviously, the rules as written interpretation is ridiculous. I keep rereading the spell and hoping I am wrong, but that really is what it means as written. I think it was written this way to be sure that you could not stack up stacks of fire damage by hitting the same target repeatedly. Whether the devs wanted Mortalbane to apply to BB's burn, or to continuous effects at all I cannot say. Nothing I can find implies that Mortalbane can or cannot apply damage to continuous effects.

As a DM:

What I would do if I had to house rule it to make sense.

1: BB damage over time effect would not stack, but the target would still take fire damage from other sources. (Obvious ruling is obvious)

2: I would let you add the bonus damage from Mortalbane to the initial strike and the continuous effect, but I would have each instance of bonus damage consume one of your Mortalbane 'Charges'. So the maximum amount of bonus damage you could get on your BB would be 10d6 per day. (With the feat only taken once)

This is probably not what the creators intended, but I think it is pretty fair and balanced.

Answer 2

Yes it does.

Brimstone blast text reads as:

BRIMSTONE BLAST

Lesser; 3rd; Eldritch Essence

This eldritch essence invocation allows you to change your eldritch blast into a brimstone blast. A brimstone blast deals fire damage. Any creature struck by a brimstone blast must succeed on a Reflex save or catch on fi re, taking 2d6 points of fire damage per round until it takes a full-round action to extinguish the flames or the duration expires. The fire damage persists for 1 round per five class levels you have. For example, a 15th-level warlock deals 2d6 points of fire damage for 3 rounds after the initial brimstone blast attack. A creature burning in this way never takes more than 2d6 points of fire damage in a round, even if it has been hit by more than one brimstone blast.

^{(emphasis mine)}

Bonus damage from a source is applied only once in any case so it would be applied only on the cast of the eldritch blast and the critical hit would only apply to the attack roll of the eldritch blast, ongoing effects never critically strike unless specified because they require no attack roll to begin with. Also you can't stack another ongoing fire damage from a different brimstone blast due to the rules of Same Effects with different Strenghts, what would happen is that you would get the new duration of the following blasts in case the victim fails his reflex save again.

So to sum it up your damage would be xd6 from Eldritch blast+2d6[Mortal bane], this is the damage of your attack, and then 2d6 of fire damage every round because the target is on fire.

Also from Stacking rules we have:

Stacking

In most cases, modifiers to a given check or roll stack (combine for a cumulative effect) if they come from different sources and have different types (or no type at all), but do not stack if they have the same type or come from the same source (such as the same spell cast twice in succession). If the modifiers to a particular roll do not stack, only the best bonus and worst penalty applies. Dodge bonuses and circumstance bonuses however, do stack with one another unless otherwise specified.

This Means that if Mortalbane damage would apply to more than one instance it would be stacking with itself on the same effect, since like I stated previously everything is generated from the same single source.

Answer 3

The phrase "A creature burning in this way never takes more than 2d6 points of fire damage in a round" in my opinion can be read "In a round a creature never takes more than 2d6 points of fire damage from burning in this way" without violating RAW. In such an interpretation, this line most likely talks about the following:

Same Effect More than Once in Different Strengths
In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the best one applies.

Even without Mortalbane, you theoretically may benefit from two Brimstone Blasts on the same target, as the best roll would apply each time (note, it still isn't greater than single Brimstone Blast's possible maximum damage).

In particular the line you have quoted makes the above rule relevant even if two or more warlocks hit you with Brimstone Blasts (or the only one present delays). Would it be Vitriolic Blast each would tic on a different initiative count so there is nothing to compare in strengths. But with that line new Brimstone Blast can't make you catch fire again - you are already burning.
_{(Maybe you may still take damage equal to the difference between two burns if the second is higher, but I don't think it was intended to require that level of complexity.)}

It is hardly intended to limit what you can do with a single use of an ability, so Mortalbane Brimstone Blast should work fine (and I believe only once per blast, but am I right or wrong on this is irrelevant for this question).

Critical hits are a different issue. Brimstone Blast effectively applies a status to the target (target is burning for X damage). Even on a critical hit it will apply just the same status, so the damage won't be multiplied even were it a straight number not a dice pool.