Good suggestions, guys!
@Ambience 327: The thing about randomizing it is that I'm not sure it's really worth randomizing. Say you used d3+2 (which has the potential to put you dangerously close to level 6 territory right off the bat). No matter what, you'll still be getting the same amount of FNP. If you get level 5, you can be a little less scared of having units get pinned when their vehicles explode, but the unit inside probably isn't going to do much all game if they lose their transport turn 1 anyway. If you get less than level 4, you suddenly lose the offensive boost these changes give wyches unless they rolled the right drugs or are hanging out with a haemonculus. So by randomizing it, you get these results:
*No effect on FNP
*Possiblity of having a turn 1 fearless army (but fearless arguably won't matter much on turn 1)
*Make wyches riskier to field
I don't know. You mentioned the advantage of randomizing it is to prevent tailoring to take advantage of the rule, but I'm having trouble picturing many ways of really taking advantage of it that don't also discourage raider spam somewhat (which I consider to be a good thing to discourage). Another thing to consider is that, because your level is only increased by melee kills, melee-heavy armies (which might mean wych-heavy armies) would have to win a combat before they started getting their extra melee oomph. Which makes it harder to assault early with them. Thoughts?
@Tagi: I thought about doing something like that. Sort of a dark eldar equivalent to Epidemus's rule. Part of me likes the idea of the dark eldar growing more powerful as friend and foe alike die around them, but it presents a couple minor issues. For one thing, it sort of encourages dark eldar to suicide attack enemies, which doesn't seem to fit them. They're less reckless chargers into melee and more arrogant-but-graceful deliverers of elegant attacks. The other issue is that with the rules you've proposed, I see your PFP level sky-rocketing very quickly. By turn 3, it would be relatively easy to have an entire army with rampage. Which isn't to say you can't have turn 3 rampage with my rules or Ambience's proposed tweaks, but to get that rampage rule, you have to have exposed your units to fire as they crossed the board, overwatch, and possibly return attacks in melee. Still, the idea of having a rising tally as the game goes on is appealing. Maybe if the levels were staggered a bit? 1 kill gets you to level 1. 3 kills total to level 2, etc.?