A Cowbell

It is an unremarkable, rusty cowbell. No marks or engravings are visible on its surface due to the large amount
of corrosion.
If a player rings the cowbell, its anomalous properties manifest. It will spawn an entity SCP-513-1 at a random
 position nearby.
This entity will silently watch the player, while staying in place.
 Viewing the entity causes the player to feel anxious. If a player hits the entity, it will disappear.
But if the player tries to sleep, the entity will attempt to approach and attack the player.