In games like Mortal Kombat Deadly Alliance, you could hold the right trigger (I own the Xbox version so I'll use that terminology here) to toggle Manual Guarding. This character I'm working on actually holds the Down Key (the character is a recreation of Powerpuff Girls D Battle in Megaville's mechanics, a flash game that is no longer playable due to Adobe Flash Support discontinuing this year).

I'm making a character which will have that feature. What I've tried doing before is copying and pasting the Guard code at around State 150 in the CNS, but it turns out that the code only manipulates the animation.

I realized instead that a simpler solution is to change the Crouch hit animations so that it resembles guarding*, then all I need to do is nullify the damage the player deals from basic attacks, specials, supers, etc.

So all I need to know then are a couple of things
1. How do I nullify damage?
2. How do I change the hitsound for each attack so that when the character is hit while Manual Guarding, it place the guard impact sound effect (the same sound effect you would hear when hitting a character that is guarding) rather that a attack impact sound effect?
3. Is it possible to implement a parrying through pressing the down key in MUGEN? Battle in Megaville's mechanics had you time your down button key presses so you could do successful parries. I know that in Street Fighter III Third Strike for instance, you could tap forward to parry an attack. I think this is possible, but I cannot wrap my head around such an implementation since I'm only in the early stages of development (and I'm not that skilled enough to do that right now).

*The velocity of the animation is not an issue here because the velocity from being hit is about the same as the guarding animation. To clarify, the attacks being dealt here in this version of the character are light attacks at the moment.