Those are my rules for a Ultra Hardcore Nuzlocke:
>Species clause: If it's the same Pokemon you find in the area and you caught it earlier this doesn't count as a new encounter, catching the same Pokemon found can break the rules.
>Typing Clause: If the Pokemon found in that area is a Pokemon that overlaps the typing of some of your teammembers, it cannot be caught otherwise it can break the rules.
>No Overleveling past Gym Leader/E4's ace: If some of your team members is above a Gym Leader/E4's ace (e.g.: Misty's Starmie) needs to be boxed until getting the badge.
>No items or held items in battle: You already know the drill.
>Rest of the rules comes from the normal nuzlocke rules from this Bulbapedia article.