How exactly does Mortalbane work when used with conjuration (especially for warlocks)?

Question

At first I thought Mortalbane was very straight-forward. An example I read is a warlock casting Chilling Tentacles. Enemies take 2d6+2d6 cold damage from the effect, plus they take 1d6+4+2d6 bludgeoning damage if grappled.

Then I looked at Summon Swarm. At first I thought it was obvious that it would work well with Mortalbane just like Chilling Tentacles. But then I started wondering: Does Mortalbane actually work with conjured creatures? The more I thought about it, I'm worried that Mortalbane only actually affects Chilling Tentacles because the spell is actually a damaging spell - the 2d6 cold damage. I started to worry that it would not actually work on other conjuring abilities at all because they are not damaging. The ability being cast is a summoning spell.

So I guess the full complicated series of questions is this:

1. If Mortalbane is used on a spell-like ability to conjure a monster, does that monster then do 2d6 more damage with everything, or does the use of Mortalbane have no effect because the actual of conjuring spell-like ability does no damage?
2. If conjured monsters do not get bonus damage, then will chilling tentacles only get 2d6 bonus damage from the cold aura, but the grapple attack will just do 1d6+4 per the spell?
3. If conjured monsters do get bonus damage, does Mortalbane also then apply to secondary effects? Does a swarm of bat's 1 damage/round bleed becoming a 2d6+1/round bleed, or does a swarm of spider's 1d3/1d3 strength damage poison into a 1d3+2d6/1d3+2d6 strength damage poison for a total of whopping 6-30 possible strength damage?

Thanks!

Answer 1

1. Conjuring a monster or a swarm is not a damaging ability, so it wouldn't have any effect. Indeed, you cannot even apply Mortalbane to such an ability, as it specifies "A mortalbane ability is a damaging spell-like ability". Player's Handbook even has a passage confirming these spells do not harm anyone on page 171:

   Summon monster I and similar spells are not attacks because the spells themselves don’t harm anyone.

2. How (and if) it applies to the Chilling Tentacles will depend on how your DM reads (or you present) the feat and the ability. There are several points which may be considered:

   • The tentacles may be considered to be conjured beings, and there is no reason their damage should be increased by the feat. (One might argue that the tentacles are the target of the spell, and thus should take the extra damage, but they are immune to damage. Also, it would be silly.)

   - Alternatively -

   • It may be argued that the tentacles spell is a creation spell (like acid fog), and the whole argument regarding conjured creatures is irrelevant. The spell creates tentacles and deals damage to the creatures who fail a grapple check, and the Mortalbane feat deals extra damage to those who fail. Or, in the case of Chilling Tentacles, everyone. There is no fundamental difference between creating tentacles and acid. This interpretation would halve all the damage against outsiders, however.

   • The effect of Chilling Tentacles is worded as "a field of soul-chilling black tentacles", which would imply the cold damage is a feature of the tentacles, and not of the spell, which would make the ability non-damaging, as noted in part 1.

   - Alternatively -

   • The field is an effect of the invocation, and there is no good reason to to attribute it to the tentacles. The additional damage applies to everyone in the area.

   • The feat is worded "deals <..> additional damage when used", as opposed to "increases damage by <..>". This may be taken to imply the extra damage occurs once, when the ability is used, and not every round. Compare and contrast, e.g. Warmage Edge (CAr p13), which says "increases damage" and Sneak Attack on spells (CAr p86), which says "deals extra damage".

   This last one makes sense from the balance perspective, as well as the rules as written perspective. I'm not sure what the counterargument would be.

   I, personally, would go with the interpretation that the damage applies once to everyone in the field, and the cold damage only is halved to any relevant creatures for the duration, but YMMV.

tl;dr - It does not increase the damage of summoned creatures, check with your DM on how it works with Chilling Tentacles, because it's really not clear-cut.