Actually, Nathaniel (originally from the Bartimaeus Sequence) might be a little OP. If I arm him with the Ring of Solomon, he has the ability to summon 20,000 spirits at the most, even to the greatest Marid or Afrit. He would be in a weakened state whenever he uses it, immobile and experiencing extreme pain. If he does summon 20,000 spirits, I think it would kill him.

The Amulet of Samarkand grants him immunity from all magical attacks (this excludes psychic, physical, Warp or atomic attacks). Gladstone's Staff grants him the power to summon a legion of greater spirits with no trouble whatsoever. The Seven League Boots grants him the ability to travel long distances in one step. If this all sounds weird and extremely OP to you, I will take some of these away.