Ok, so I currently use Huzuni, have tried most clients, and have a basic understanding of how they are coded. What I don't understand is a few people on the server I play (DesiredCraft) are able to add more damage to their hits? I have already tried inquiring them to tell me but they say they don't use a hacked client(Obvious lie is obvious). For example, they hit me once, and I am damaged 3 hearts, where normal damage caused by one swing is 1/2 - 1 Hearts. It's as if they have a strength V potion(which don't exist in vanilla). But when they turn on their kill aura,(Plus their damaging increase hacks) they can pretty much clear a whole room of people.

So can anyone tell me what client can do this or explain how one can code such a beast?

(Not asking how do make a client, just how the damage increase works)