For a while now I have been wanting to make a power fist that could either knockdown or knockback an opponent on a critical hit. I am not quite sure how to go about implementing this though. I could use some help.

Well there are a couple of ways to do this. The knockback effect is, I believe, an all or nothing effect; either you have it on your weapon or not.

For the knockdown effect the tried and true way is to damage fatigue. This can be done a little bit on each hit a set or random amount or it can randomly cause a set or random amount of fatigue damage. Off the top of head I couldn't tell you if it can be timed to coincide with critical hits, I'd have to research that a bit.

Once you have your methodology decided you need to write an effect script, create an effect and put it on the powerfist.

Hope this helps.

I think you are thinking of Oblivion. There is no fatigue damage in fallout 3 to my knowledge. How the effect is implemented on a critical hit is that for each weapon there is a spot to add an effect that activates on a critical hit, and then you can also select whether or not it only happens on death. This is how energy weapons burn up enemies or turn them to goo on death, and how the victory rifle and gauss rifle knock down enemies whenever they score a critical. I tried telling a power fist to use the victory rifle knockdown effect on any critical hits but that didn't work, so I need to figure out how to make an effect that I could use in that certain field on the weapon stats screen in the geck that would accomplish my goal.

Fatigue is there, it's just not used in the game. Try opening the console and typing:

Player.damageav fatigue 200

Your player will drop like a sack, the higher the damage the longer you stay down. I used this in my Crippling Injuries mod, it works really well.

I didn't remember about the On Critical Hit option for weapons, it's been a while since I played with weapon effects.

After retrying my previous idea of adding the victory rifle knockdown effect to a weapon I found it does work like it should. I don't know what might have gone wrong before. I decided to retry it after noticing that the Electro-Suppressor from MZ used the victory rifle effect for it's knockdown.

I changed plans and made a hammer for my next character that will be named Thor. This Super Sledge has the DOT effect of Jingwei's shocksword, and the knockdown effect of the victory rifle. I tested it and it all works.