can some tell me a decent distance to put it on, for doing really anything.
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*trigger happy*
I managed to do one in three years.

Decap is just about accuray.

if your strike is accurate, right at his neck, you got a clean decap.

decap isnt always luck when someone get his hand in ur neck then he rais his arm and contract wrist,elbow that will 100% decap u

If you are lookin' for a decap aim for the neck area, and hit the neck with your hand, or foot which are the easiest to decap. But make sure you build up speed with the joint you want to hit the neck with, you can do this by moving the abs, rotating the chest, or extending ankles to jump higher etc. So strike the neck with a powerful move and you will always decap, and if you don't get it right the first time you can always press "R" to play your replay again, and press "E" where you think you can improve and if you want to see both ghosts to see how strong or hard your hitting press "B" to see both Ghosts.

Hope this helps.

Usually it's about speed,accuracy and force.For speed you need to punch or kick in a faster speed.Accuracy you need to edit your kick/punch decap to hit the right spot.Force is strength usually gets stronger when you speed is faster.Thats how I do it
Hope it helped you a bit.

Get your arm on the side of the head. Contract elbow and contract wrist. Or if you want to kick it off look at some replays like nuthug's replay. Extremerunedit It show's you an example of a good kick decap with style.