The FAQ indicates that if you use ICSs or Grendades with the intent to catch a target in the blast radius then the target gets an opposed roll (rather than a success test), but how would this apply in a blind-fire situation? I can easily see my group running into a situation where they know for a fact that there are hostile targets they cannot see, such as some security guards taking cover around a corner. They may not know exactly how many guards are around the corner, or how close they are to the edge, but they like to blow things up so they decide to toss a grenade (or fireball) down to the end of the hall. In the case of grenades, I'm assuming the -6 modifier would apply for blind-fire, but would that also apply in the case of a spell?

For grenades you are aiming for a specific spot, and your successes would determine how far away from that spot the grenade bounces. You would get the -6 blind fire penalty to try and hit the spot, but it wouldn't be an opposed test. The opposed test only happens if your trying to get it to land point blank in a targets spot, where they could dive out of the way/knock it away.

I'm not sure about the penalty for the indirect spell. Blind fire would make it difficult to target the exact location you are hopping for, but on the other hand, distance from the point of origin of an area spell is irrelevant as long as they are caught in the blast(being 4m away from the origin of a force 5 fireball is the same as taking it point blank), so I would say that the darkness is irrelevant, but I have to rules to support that.

I'll have to look at the faq again. My GM seems to ignore that and just go with the success test, (because c'mon, how are you going to dodge a grenade?) but I guess it makes sense if you consider that you're aiming at a target, and the target is moving. (So your grenade lands further away from them because they got the drek out of there, not because you missed.)

In light of that you might want to apply scatter rules to the person instead of the grenade, with the target's net hits moving them further away from the target point.

I think the grenade rules were written this way to prevent people from abusing them by always aiming for the ground rather than the person, but a blind fire situation is one of those things that pokes a hole in it. By RAW I'd say you have to try and peg one of the guards in the forehead, using blind fire rules, but I'd suggest just making a success test to hit the middle of the hallway, and pretending you don't know the guards are there.

Or you could let the guards roll against that to increase their distance from the grenade by 2 meters per net hit, (4 for aerodynamic and launched grenades) up to the maximum rolled scatter.

In fact, that seems like a pretty good houserule for grenades in general, I'm going to run it by my GM.

Isn't there a -2 Defense pool penalty against AoE attacks, like grenades and Indirect spells?

Not that I'm aware of...

>checks<

You're right, there is. Also, if the guards around the corner are unaware of you, it's treated as a success test anyway.