Is there a secret karma system?

[Vantalane]

I've been playing witcher 3 for a little while now and after I have done the main quests and most of the side quest I got bored and started to look for some challenges.

So since the city guards have a standard of being a higher level of the player, I started messing with them to enhance my skills.
Do I loose some ''Karma Points'' when I kill them and just go on? And do you know some other challenges to do?

[nochat]

Well said. ^

[v0]

Yeah guards're one challenge and you can control how many you take on at once. No loot no XP though so not encouraged at all just satisfaction if you beat them. There's archgriffin on island in Skellige (NE part of map) that's also challenging but everything else rather straightforward in vanilla game once you get hang of it. Some enemies in expansions come with interesting combat mechanics and at least one achievement there require you take on like 6 enemies at once.