Skeleton

Skeletons are monsters that spawn underground in the stone layer. Skeletons occasionally drop hooks, but they are uncommon. Skeletons may run away after their health is below 15.

Skeletons can break down a door, even when there is not a Blood Moon , but since they only spawn in the stone layer, it shouldn't be a problem if you build a house on the overworld.

If a skeleton cannot get to the player for a certain period of time, he walk away. If he cannot get away for a certain amount of time then he will go back to trying to get to the player. This cycle continues until he either walks off the screen or is killed. If he manages to walk off the screen, he will despawn automatically.