Here is the fighter mechanic I developed earlier this year for BX (and its retro-clones Labyrinth Lord and Basic Fantasy RPG) that I call the damage dice system.
I bring this system up to express some ideas about how the XD system could be done better IMO.
This system is very similar to the XD system for DDN but was (initially) developed independently. The basic system (outlined below) has been tweaked but in generally what I developed prior o the XD system being published. The advanced system has been heavily influenced by the XD system. I envisioned something along these lines bak when the basic system was developed but luckily WotC did the heavy lifting for me.
The basic system works like this. Fighters and similar classes (dwarves, elves, and halflings) get 1[W] to use on weapon attacks every round at first level and it increases to 2[W] at 3rd, 3[W] at 6th, 4[W] at 9th, etc. Clerics increase damage dice (i.e. [W]) every 4th level (2 at 4th, 3 at 8th, etc.).
These dice can be used to make an attack against a single opponent or can be split up to make attacks against multiple opponents. For example, a 10th level fighter can make one 4[W] attack, two 2[W] attacks, four 1[W] attacks, one 2[W] attack and two 1[W] attacks, etc. Each attack must be against a different target and all damage modifiers apply to each attack.
For the advanced system the character can trade in damage dice to perform special maneuvers. So far these maneuvers are:
Parry - when hit by an attach you can reduce the damage done by rolling 1d6 for each [W] spent and adding the total. If equipped with a shield you can roll d10s for this maneuver.
Defend - when an adjacent ally is hit by an attach you can reduce the damage done by rolling 1d6 for each [W] spent and adding the total. If equipped with a shield you can roll d10s for this maneuver.
Composed Attack - by spending 1[W] you can cancel disadvantage you have on an attack.
I am still working through the advanced maneuvers but you get the idea. The advanced maneuvers would not be open to clerics, just fighters, dwarves, elves, and halflings.
I like using the weapon's damage die for the XD and allowing shields to parry and defend better. Even though I also like the idea of a physical die to spend for maneuvers, I think the system would work better by varying the die based on maneuver and weapon used. This does add complexity but the basic system is available to those that want to keep it simple.

This system is very similar to the XD system for DDN but was (initially) developed independently. The basic system (outlined below) has been tweaked but in generally what I developed prior o the XD system being published. The advanced system has been heavily influenced by the XD system. I envisioned something along these lines bak when the basic system was developed but luckily WotC did the heavy lifting for me.
The basic system works like this. Fighters and similar classes (dwarves, elves, and halflings) get 1[W] to use on weapon attacks every round at first level and it increases to 2[W] at 3rd, 3[W] at 6th, 4[W] at 9th, etc. Clerics increase damage dice (i.e. [W]) every 4th level (2 at 4th, 3 at 8th, etc.).
These dice can be used to make an attack against a single opponent or can be split up to make attacks against multiple opponents. For example, a 10th level fighter can make one 4[W] attack, two 2[W] attacks, four 1[W] attacks, one 2[W] attack and two 1[W] attacks, etc. Each attack must be against a different target and all damage modifiers apply to each attack.
For the advanced system the character can trade in damage dice to perform special maneuvers. So far these maneuvers are:
Parry - when hit by an attach you can reduce the damage done by rolling 1d6 for each [W] spent and adding the total. If equipped with a shield you can roll d10s for this maneuver.
Defend - when an adjacent ally is hit by an attach you can reduce the damage done by rolling 1d6 for each [W] spent and adding the total. If equipped with a shield you can roll d10s for this maneuver.
Composed Attack - by spending 1[W] you can cancel disadvantage you have on an attack.
I am still working through the advanced maneuvers but you get the idea. The advanced maneuvers would not be open to clerics, just fighters, dwarves, elves, and halflings.
I like using the weapon's damage die for the XD and allowing shields to parry and defend better. Even though I also like the idea of a physical die to spend for maneuvers, I think the system would work better by varying the die based on maneuver and weapon used. This does add complexity but the basic system is available to those that want to keep it simple.