I have previously discussed good and bad points of the minion rules in D&D (here, here, then here). Now I will mention the scale I am currently using to estimate how powerful a minion should be (in response to a blog post here).
Here are the basic statistics I am using for a heroic level melee-only minion:
AC: 14 + level
Fort/Ref/Will: total = 34 + 3*level
Attack Bonus: 5 + level
Initiative: ¾ * level
Damage: 3 + level/2
These stats are mainly based on a combination of looking at the DMG and looking at how minions are actually designed in the monster manual. The first three values are just what I use for the typical normal monster, and the initiative is just 2 lower (minions have low initiative). Damage is half that of a normal monster.
How minions scale with level is tricky, since I’ve noticed they become weaker as you gain levels and have more minion-killing abilities. I’ve been giving a 5% bonus to the minions for every level over 3 (meaning they have some special power or other perk that gives them that much greater offense or defense than otherwise calculated). I’m not sure that isn’t too weak of a bonus, given the trouble minions seem to have staying alive against high level characters.
As for the XP value, I’m currently estimating that a minion should cost 1/6 as much as a normal character, due to their extreme vulnerability to area effect attacks.
Heroic-level minions are fun. I haven’t tried a lot of minions at Paragon and Epic levels. I’m afraid the players will gain so many anti-minion powers that minions don’t work well any more.
Note, however, that ranged minions are much more powerful and less vulnerable than melee minions, since they can try to disperse as much as possible and avoid mass death from area effect attacks and a lot of minion-killing powers.