I plan on using these rules in the Mortal Combat encounter of First Sanction (I am also creating a similar thing for Warhammer Fantasy 3rd edition). This is part of the preparations I'm doing for running this scenario for some friends in my gaming club (I'll post the preparations once they are ready... I'm getting close, it'll depend on the amount of real life job I have these coming weeks). As usual, constructive criticism is highly appreciated (specially if you have tried something similar and saw it fail miserably):

Duel Rules

Combat proceeds as normal (with Initiative rolls, number of actions, etc.) except for the following extra changes and new rules that will make it a bit more tactical for some added complexity.

Changes to already existing rules .
• The Feint action works differently in duels. If the attacker is successful, the defender has a -10 penalty to his Dodge or Parry; each extra degree of difference gives an extra -10 penalty.
• If the Parry or Dodge is successful, the attack still deals damage but some of it is cancelled. The amount of damage cancelled is equal to half (rounded down) the result of the Parry or Dodge Test.
• Called Shots are not allowed in a Duel (as explained below, there is a new mechanic).

New rules for Duels .
• Both participants in the duel get two extra 1d10 dice of different colors. One will be used to secretly mark the direction of their attack, the second will be used to mark the direction of their defense, using the following table:

0 Head
1-2 Arms
3-6 Body
7-9 Legs

• In the first combat turn, any number may be chosen. After the first attack, the choice is limited following the following table. If, either by choice or mistake, the attacker does not follow this table, he'll suffer a -20 penalty to his Weapon Skill (it is difficult to direct consecutive attacks to parts of the victim that are not close to each other).

Previous Attack Next Attack
Head Head, Arms, Body
Arms Arms, Head, Body
Body Any
Legs Legs, Body

• Before deciding how to place his Defense Die, the defender tries an Ordinary (+10) Awareness Test. If the test is successful, and for each degree of success, the defender may ask the attacker whether he is using a certain number in his attack die.

• After both the Attacker and Defender dice have been selected, they are revealed and the following modifier is applied to the Parry or Dodge test of the defender:

Relative result Modifier
same number +20
different number, same area +10 - ( number difference times 10 )
different area - ( number difference times 10 )

• Then, as usual, the Attacker checks his Weapon Skill ( remember the possible -20 penalty if he changed target too much ), and the Defender may roll his Parry or Dodge with the appropriate modifier. Damage is calculated taking into account that some or all of it may have been cancelled by the Parry or Dodge test (remember, half the result of the test, rounded down).

• Depending on the area hit, the damage will also have the following modifiers:

Head: extra 1d5 damage (no Righteous Fury for this extra damage); target must pass a Challenging (+0) Toughness Test or be Stunned for 1 Turn
Arms: target must pass a Challenging (+0) Toughness Test or suffer -10 penalty to his Weapon Skill for 1 Turn
Body: no extra effect
Legs: target must pass a Challenging (+0) Agility Test or fall Prone

• At the end of each combat turn, both combatants must pass an Ordinary (+10) Toughness test with a penalty equal to the number of combat turns already played. A failure means that combatant takes 1d5 damage ( no armor or Toughness reduction ) and 1 level of fatigue ( in my campaign, each level of fatigue gives -5 penalty to all rolls ).

Optional Rules .
You may add even more complexity to the duel if you think your players will find it fun, and to have some extra spice to the combat.

a. Special Events . If the attacker rolls doubles in his Weapon Skill test, roll 1d10, look to the table below and apply the event accordingly ( if the attacker missed his roll, he is the losing party; otherwise, the defender is the losing party ):

1. Difficult Terrain ... slippery ground, earth trembles, or similar... The losing party must pass an Ordinary (+10) Acrobatics Test or a Challenging (+0) Agility Test or fall Prone
2. Hard Push ... the combatants crash as two trains and one of them may lose foot... The losing party must pass a Challenging (+0) Strength Test or fall Prone
3 Weak Spot ... if the losing party is the defender, his armor is reduced 2 points in this attack... If the losing party is the attacker, his weapon is lightly damaged and will do 1 less damage for the remainder of the combat (until he can do some basic repairs)
4 Overexertion ... the losing party must pass a Challenging Toughness Test or gain 1 level of fatigue and take 1d5 points of damage (no reduction from armor or Toughness).
5 Footwork ... until the losing party wins a Manoeuvre action, the winning party has a +10 bonus to his Weapon Skill Tests
6 Mind Games ... until the losing party wins a Scrutiny vs. Deception Test (he can try as a Half Action), he'll suffer a penalty of -10 to his Awareness checks
7 Ringing Blow ... the losing party must pass an Ordinary (+10) Toughness Test or become stunned 1 Turn
8 Clash of Titans ... both combatants clash their weapons and push with all their strength... conduct an opposed Strength Test, the losing party having a -20 penalty to his roll; the loser of this roll falls Prone and suffers 1d5 damage (no armor or Toughness reduction)
9 Lightning Strike ... the winning party may immediately carry out one attack for free with a -10 penalty to his Weapon Skill Test
0 Disarming Strike ... the losing party must pass a Challenging Agility Test or be disarmed, his weapon falling 1d10 meters in a random direction (use the Scatter rules for grenades to decide direction).

(the beauty of the above is that you can always add new events to the table)

b. Footwork . Keep a tracker with one Neutral position and several positions to either side ( people playing Warhammer Fantasy 3rd edition will know what I am talking of here ). Each time a combatant wins a Manoeuvre Test, advance a counter in the tracker to his side. Each position towards the side of a combatant from Neutral gives that combatant a +10 bonus to his Weapon Skill Test... this represents the footwork and manoeuvres each combatant tries to gain the best position, and you can describe the combat in that regard (maybe using high ground, or fighting with the sun behind you, etc.)