How do attack penalties stack?

Question

I'm looking for the exact number of "-to hit", if attacking one of my allies, that would be applied. I'm creating a Psion/Swordmage hybrid and I'm wondering what my collective debuffs would be under various situations. My big concern is I don't entirely know how my feats and my summoned creatures interact with the stacking of negatives. I will have the following feats: psychic lock (phb1) & mark of warding (Ebberon phb). I have the following paragon path: Dreamwalker (phb3)

What would be the total -to hit if I cast Dishearten(unaugmented) & I have the monster marked by swordmage shield aegis mark (forgotten realms phb)?

What would be the total -to hit if I had attacked a creature with my summoned creature "Summon Phantasmal Killer" (PP page 90) and hit with his standard melee attack?

Lastly, what would be the total -to hit if I had caste Dishearten (unaugmented) on the creature I had previously marked with my Swordmage shield aegis & then my summoned creature from my paragon path Dreamwalker called "True Dream Form" did his instinctive effect: casting dishearten himself on the same creature?

Answer 1

Well let's look at all of these one by one and we'll evaluate things as they come up.

The first thing you need to know though is that debuffs always stack unless they are coming form the same power. With that in mind let's look at at each power you've mentioned and inspect it individually.

The first one that we need to look at is the mark generated by the swordmage's aegis. All marks have the same debuff, -2 to hit any ally when they attack with a power that does not include you.

Psychic Lock inflicts a -2 penalty to the next attack roll. This stacks with the mark.

Mark of warding makes your mark a -3 instead of a -2. So attacking the target of your Aegis with a psychic power inflicts a total of -5 to attacks against your allies that don't include you, and a -2 against you, for their next attack.

Dishearten unaugmented against the target of your Aegis would have a net effect of inflicting a -7 penalty on his first attack against someone not you, -5 on subsequent attacks not you, -4 on the first attack vs you, and -2 on subsequent attacks against you during the round. Not your aegis is -4 on first attack, -2 on subsequent attacks during the round, regardless of target.

Phantasmal Killer has an identical effect against as above to your Aegis target.

The final case will have the same result as the debuffs from Dishearten do not stack. (the net -4 on first attack, and -2 on subsequent attacks do not add as they both come from the Dishearten power). Were you to find a different psionic psychic power that debuffs (say Mind Wipe) that would stack, though you would not benefit from psychic lock the second time.