if you charge then immediately right after that you can pull a lightening attack.....
No you can't. First of all, charging is a full action, so no half action left to lightning attack with. Secondly, if he's already delivered two sets of swift attack via the charge, he's used both of his dual-wield attacks, thus he's out of attacks. Third, that's performing two separate actions with the attack subtype, which is prohibited.
Also, with a WS of 40ish (judging by the damage from Crippling strike, which is half of his WS bonus) he's capped at 4 attacks per swift attack, which would require 8 DoS. While he might score more with enough bonuses, he can't get more hits in. Multiple hits from both Lightning and Swift attack is capped at your WS bonus. Thus, two-weapon wielding with Lightning claws would score him a maximum of 8 hits.
come to think of it- what does the "special" special rule say? I cant seem to find it in my book.....
It's listed under the Lightning Claw entry. Basically, when wielding one, each DoS adds +1 to the damage. When wielding two, it adds +2 per DoS. How this combines with Lightning attack is unknown IIRC. Certainly not clear from the text itself.
real fast since I missed it: does the AP and TB actually get applied to each HIT or per attack? or totalled up at the end?
Per hit. So of those 24 damage hits, it would have soaked up 14 points from each. Furthermore, while it lacks the skill, if it had a reaction it could have either dodged or parried at -20 for being untrained (or -30, too tired to check). Which, since both characteristics are at 55, might have removed a hit or two. Remember, it's not a true opposed test, but rather one where each DoS negates one hit.
Also @Adept Orcadius in the previous editions of 40k melee attacks weren't affected by size modifiers, so thats -40 from your example case, I think that is still true in BC but might want to check.
The BC rules do not, as far as I can see, make any mention of the to-hit bonus/penalty from size only applying to Ranged weapons. Which, considering the general unification of the ranged and melee rules, I'd probably call an intended change.
As for the OP's question that combination does sound extremely potent, but not unbeatable. most important things to remember is to be strict with psychic powers, for every power he is presently maintaining he takes penalties on further power checks like killing will, so if he is PR6 and maintaining 2 powers I think he is only PR 4 for killing will. Also I believe in deathwatch it was errata'd that killing will could only be used on 1 hit per turn because it was a focus power test just to make sure you are using that correctly and finally perils and psychic phenomena rolls arent skill or characteristic tests, so the can't be affected by infamy. roll them behind a GM screen and make sure he realises that using 3 powerful psychic powers comes with a price from the warp.
Few not trues there. The sustaining penalty is most likely only for other sustained powers. Secondly, it only kicks it when sustaining two or more powers, which is not needed for most warp-time using sorcerers, unless they're throwing in telekinetic shield or something. Regardless, killing will would most likely be unaffected.
The Deathwatch Errata also isn't really applicable. You can manifest killing will with every hit, since it's A) a free action and thus not bound by the "two different half action" rule and B) subtype free and thus not bound by the "No more than one attack or concentration subtype action per round" rule. However, house ruling a maximum amount per round is not a necessarily bad idea. Or, more deviously, preventing it's use while fettered. 10% chances build up quickly . Also, here the +X to psychic phenomena penalty of sustained powers WOULD kick in.
What I am trying to say is try challenging them not with one giant monster, but with a tactical army instead, with certain enemies tailored to each of them to fight.
I endorse this! Tailored, tactically aware and diverse enemies are not only far more credible threat, but a lot more fun to fight. It allows players to get to react to unusual tactics rather than merely dodging the same lumbering beast's lethal blows, it makes them feel useful because there's something for them to "contribute" to and it also helps create fantastic spotlight moments for every character, with the psyker engaging in a tense battle of the minds and warpflame, the melee guy having a pitched and tense duel atop the wreckage of the entire tank battalion eradicated by the anti-armor specialist.