Attack Stunt
Attack Stunts work like this:
Using the Fast Stunt Challenge
Fast stunt works the same way, except:
The rules indicate that you can make a fast stunt "while still gaining a full attack action", but I'd also allow it if someone wanted to use a fast stunt and then only make one attack and move their full speed (instead of the at-best half speed an attack stunt normally allows).
Q: What is the down side to attempting an Attack Stunt?
An Attack Stunt requires a full attack action to inflict one attack which might gain a bonus to attack or damage. This means that if you normally have iterative attacks, you don't get them, which is obviously a big loss of firepower. You can always try for a Fast Stunt to get your full attack routine, but if you do, there is a penalty for failing the check (-2 to your attack rolls).
If you don't yet have iterative attacks, you still suffer reduced movement (half your base speed at best, possibly no movement at all, depending on the skill used for the stunt), which limits your tactical options.
Disrupting Attack
When using a base attack check to make a disrupting attack stunt, you inflict only the base weapon damage. No other bonuses for damage (Strength, sneak attack etc) apply.
Q: Can you use Disrupting Attack to disrupt class abilities?
This stunt can be used to prevent a character from using an extraordinary or supernatural ability. Most class abilities in Iron Heroes are extraordinary abilities, so they would be affected by this stunt.
For instance, you could use a disrupting attack stunt to stop an Archer from using Killing Shot for 1 round.
For ease of play, I'd recommend that currently active multi-round abilities (such as berserk strength) are merely suppressed for the round (your attack cuts across his arm, momentarily weakening his strikes) rather than being completely negated and needing to be restarted next round.
Stunts and Harrier Movement-based Bonuses
See the Harrier for details.
Setting Stunt DCs
Q: What kind of difficulty should I be setting for stunts with a first level party? Should most of them be directly opposed checks, or fixed DCs?
I strongly recommend making all attack and defense stunts use opposed checks, because then the DC is never an issue. If you don't feel an opposed check is appropriate, I'd make the DC to inflict the minimum level effect somewhere in the 15-20 range, and modify the DC upward for larger effects based on the individual stunt descriptions. But Stunts are freeform for a reason: do whatever works in your game. There is no 'right' or 'wrong', really.
Negative Consequences for Failed Stunts
Q: Is it fair to impose failure penalties for the stunt check, if it makes sense in context? So, if the harrier jumps off a roof and tries to decapicatate a guard, but blows their Jump check, should they, say, still get to make the attack but fall prone?
If your players are OK with it, it is. Personally, I wouldn't do it: it might discourage some players from using stunts if there is a negative effect associated with failure (the "I'm better off just making a normal attack" syndrome)
Situational Modifiers for Stunts
For stunts that are based on Base Attack Checks, use the normal modifiers that apply to attack rolls (for instance, a Miss Chance would be appropriate against an Invisible opponent). For stunts based on skill checks, see the Situational Modifiers entry in the Skills subject for details.
Inflict Penalty
The Inflict Penalty stunt is a standard action.