Every Teddy Bear that is truly loved by a child becomes his or her guardian against the terrors of the night.
And as long as the child truly loves the bear, then the bear cannot loose.
But when a child no longer loves his/her bear, then the poor creature continues its fight against an ever growing foe, but without the power derived from its bond with a child. When the bear finally looses, it is transformed, literally turned inside out, by the terrors of the night into the warped and pathetic creatures known as Terror Bears.
Terror Bears are usually found in locations once inhabited by children (schools, hospitals etc), where they will sit completely inert for years at a time until they are disturbed. When that occurs, they will latch on to the person who disturbed them (or the nearest child, or child-like person), and begin to terrorize them in their own warped quest for affection. This attention begins with minor scares and can escalate to gruesome murders as the Terror Bear desperately and psychotically attempts to reestablish some sort of bond with a person, even if is only one of absolute fear.