Werewolves

If you haven't noticed, the moon in Minecraft rotates through phases.
This mod allows the moon to have some functionality within the game, as well as makes nighttime slightly more hostile toward the player.

During a full moon, anyone with the mod installed will hear a howling sound, and all untamed wolves will become hostile and attack nearby players within 8 blocks until the night is over.

Remember, they are wild wolves, not domesticated dogs, and this mod helps them live up to that name.

The mod will work when installed on servers, however, the client must have the mod installed to hear the wolves howling.