“In the land of the sewers where the rat king lies. The dark lord Rat Sauron forged for himself the one ring in which he poured his hatred, malice, and the will to dominate all the rats of middle earth. One ring to rule them all, one ring to find them, one ring to bring them all, and in the darkness bind them” -The Lord of the Rats 

The Ring of the Rat King has been cursed so that none would wield its vast and terrifying power ever again. Once the ring has a new owner it cannot be taken off, it can only be destroyed in the stench of the sewers from where it came. Each day the unfortunate owner must roll a d20. The number on the die is the number of rats that will follow you around for the day. The owner also receives disadvantage on  investigation checks...because of all the rats. 

Notes: Disadvantage: Investigation