You will find all this information elsewhere (some links at the end), but I though it would really help some people to have it all one place
These rules regarding handling minion groups include stuff our group got wrong at some time or other.
So, if I have made any mistakes, please let me know, and I will make corrections. Thanks!
Minions and Soak
Soak of a minion group is only subtracted once when you hit the minion group. The rest damage adds to the total wounds of the group.
Example: 3 storm troopers, each have 5 soak and 5 wounds, are hit for 15 damage. Then the minion group suffers 10 damage.
Defeating Minions
When minions are defeated you do not reduce the total wound threshold of the group. Instead, you add the wounds to the current wound total of the group and the group looses the benefit (ranks) of the minions that have been defeated.
Taking the example of 3 storm troopers from above: the minions have a combined wound threshold of 15. This is how the various wound levels effects the minion group:
Current Wounds: Effect: 1 - 5 All minions OK = 2 skill ranks 6 - 10 2 minions OK = 1 skill rank 11 - 15 1 minion OK = 0 skill ranks (but still able to act) 16+ All minions defeated
Blasting Minions
One minion takes the initial hit, but the minion group suffers the initial damage as usual (i.e. soak once, and the rest of the damage applied to the group). Each remaining minion (excluding the one initially hit) is then hit by the blast damage. This damage is first soaked (once for each hit), and then the remainder applied to the group.
Note that the number of successes rolled are also added to the blast damage.
Example: the storm troopers above are hit by a damage 8, blast 5 grenade (and the blast effect is triggered). The number of successes rolled is 3. Initial damage is 11 (8+3) - 5 (soak) = 6. This means that one minion is defeated by the initial damage (this is the minion that was actually hit, so there are 2 minions remaining).
The remaining troopers are each hit by the blast so they each receive 8 (5+3) - 5 = 3 damage. So the group gets an extra 6 (3x2) damage in total. As a result the minion group has taken a total of 12 (6+6) damage. Now there is only one minion remaining.
Engaged Minions
Minions are not necessarily engaged. In other words, it is quite possible for a minion group to "fan out" so that they are not engaged as long as there is enough space to do this. This is determined by the GM, of course.
If the minions are not all engaged then, as usual, a blast can only be applied to any part of the group that is engaged. I assume the "sub-group" can be selected by the attacker.
Critical Hits
Only one critical hit is allowed per hit. This means that multiple Crits against a minion group is not possible with one hit (in general, an extra Crit just means a more powerful Crit).
If minions are caught in a blast then an extra Crit per blast hit is possible. And, of course, repeating weapons that hit multiple times also allow one Crit per hit.
Some forum posts suggest that GM may allow an extra Crit against a minion group per triumph rolled. This is not a hard rule so the GM may make it dependent on the situation.
Edits
Edit #1: (thanks to kaosoe's comment below) Skill ranks were counted incorrectly. I was counting 3 minions as having 3 skill ranks, 2 as having 2, etc. This is not correct. Only the minions after the first one add skill ranks.
Edit #2: (thanks fatedtodie) I was referring to the minions as killed, but more accurate is to say they are defeated. As fatedtodie explains below, whether the minions are actually killed is at the GM's discretion.
------------------------------
Here are some links with further details on this topic:
http://community.fantasyflightgames.com/index.php?/topic/114411-minion-groups-hit-by-crits-and-blast/
http://community.fantasyflightgames.com/index.php?/topic/108101-ffg-developer-answered-questions/
http://www.fantasyflightgames.com/edge_minisite_sec.asp?eidm=232&esem=4