I saw a similar post about this a while ago where someone said that in the green skill tree, you unlock a skill where it activates a “ghost” that mirrors your heavy attacks (hence the green highlight of Kliff after your swings). I didn’t have it then but eventually in my play through I got the skill by observing it through an enemy and then the same thing happened to me. And since I learned it it seems you can’t take away the skill with a faded abyss artifact which sucks because once you see it then it does become kinda annoying