Karma is a gameplay concept that encourages people not to mine other players' items and not to kill other players with bombs (except in PvP worlds).
Players decrease their karma level in a couple ways:
- Mining blocks that belong to other players (specifically, other players who have not friended the mining player). Generally, you can avoid losing karma this way by only mining blocks that spawned with the world. These are identifiable by their general state of decay or their layout - you can start to recognize spawned houses and dungeons the more you play.
- Bombing other players in non-PvP worlds.
Players receive several warnings before their karma bottoms out. Once bottomed out, players cannot mine or place blocks until their karma restores somewhat.
Karma recovers at a slow rate while in-game. If a player has bottomed out their karma, they will need to hang out in-game for a while before it returns to manageable levels.