Your alternate wording is fine, and we may mention that even creatures immune to paralysis are affected.
I know there are precedents, I'm mostly just trying to simplify this spell a bit. If you want to keep the limit, no problem.
I guess we're keeping all 12 properties, in that case. Care to write a draft?
Well I'll give it a start.
Binding Circle
Conjuration (Summoning)
Level: Goat 2, Sor/Wiz 3
Components: V, S
Casting Time: 1 minute
Area: A circle with a radius up to 1 ft. per level
Duration: 1 day/level
Saving Throw: Will negates (see below)
Spell Resistance: No
This spell creates an invisible magical trap that can restrain an undead creature or a creature with the Extraplanar subtype. The caster must trace out a circle and mark it with runes that identifies what creature the
binding circle will trap, either by type, subtype, species, or truename (e.g. "Undead", "Tanar'ri", "Lantern Archon", or "Rexpluff the Dust Mephit"). The circle and its runes are clearly visible to any creature using
see invisibility,
arcane sight or
true seeing.
The
binding circle is triggered when a creature that matches the rune identification attempts to exit the circle. A
binding circle can trap multiple creatures with the same identification if they are all within the circle when it triggers, providing their total Hit Dice does not exceed the caster level of the spell. If the triggering creature(s) have more Hit Dice than the spell's caster level, the
binding circle automatically collapses and is dispelled. Less powerful triggering creatures must succeed at a Will save or be bound by the spell. If the
binding circle's caster level is more than twice the Hit Dice of the triggering creature, it increases the save DC by 2.
A victim bound by the spell is immobilized and helpless, but can still perform purely mental actions. Victims instantly regain mobility if they leave the circle, either by being carried out by allies or by using a purely mental transport power of their own, such as a still silent
ethereal jaunt spell or the
psionic dimension door psionic power. The
binding circle will end if all the creatures it has trapped leave its circle. If they don't escape the circle, they remain immobilized until the spell is dispelled or its duration runs out.
A
binding circle can only be triggered once. Other creatures of the specified target class can freely enter and exit the circle once it has been been triggered.
A spellcaster can have only one
binding circle spell at a time; if a second is cast, the first one (if still active) is dispelled.