What you want is the Nightmare Creature template. What I've linked here is a Nightmare Ettercap, but there's a description of the template there as well.
One of the powers of a Nightmare Creature is the Night Terrors:
Night Terrors wrote:
Once a nightmare creature enters a target’s mind with its dream or nightmare spell-like ability, it can attempt to control the target’s dream. If the target fails a Will saving throw, it remains asleep and trapped in the dream world with the nightmare creature. Thereafter, the nightmare creature controls all aspects of the dream. Each hour that passes, the target can attempt another saving throw to try to awaken (it automatically awakens after 8 hours or if the nightmare creature releases it). The target takes 1d4 points of Charisma damage each hour it is trapped in the dream; if it takes any Charisma damage, it is fatigued and unable to regain arcane spells for the next 24 hours. The target dies if this Charisma damage equals or exceeds its actual Charisma score.
That gives you a creature that can cast Dream or Nightmare 3/day, a Fear Aura and Frightful Presence, and can force a sleeping victim to not wake up for hours while the victim suffers Cha damage. They also have Shadow Walk 1/day to escape and constant Protection from Good for a defensive boost.
Imagine adding that template to a Sandman elemental. This creature has a 20' Sleep aura at a CL8 with a DC 14 Will save, but you could always pump that higher if needed. Their attacks also induce Sleep as well. Both effects have no upper limit of HD affected either.
The sandman can force 1 or multiple opponents to sleep, then trap them in the dream with Night Terrors. They might even be able to cast Nightmare during Night Terors, so even if the victim(s) wake they could potentially have taken Cha damage, 1d10 HP damage, and be exhausted, with Arcane casters unable to recover spells for 24 hours. I don't know if you can cast a spell while also using Night Terrors, but throwing it out there anyway.
