The necromancer targets the soul of one or two enemies. The two enemies are bound by their souls and cannot move further than 60 feet from each other (to also restrict teleportation and plane shifting).   Additionally, when a spell targets one of the enemies it duplicates the effect onto the other enemy, regardless of range. This does not duplicate area of effect spells unless they specifically target specific enemies such as the spell Slow. If the spell is only casted on one enemy, the first enemy to come within 60 feet of the targeted enemy is then bound to the first enemy.