Hmm, here's going to be another variant. As far as teleportation, I'd rather allow a caster level check every time or not at all. The once per day bit seems too exception-based and fiddly.
I like the idea of the consecrate or hallow spells, but hallow isn't going to help much since it has a 24 hour casting time. (Consecrate is fairly expensive, too, though it at least only takes a standard action to cast.) I'm uncertain about requiring a save to exit, though; maybe it should just let the victims out.
Here's my stab at it:
Shadowtrap Aura (Su): A ghost-stone continually projects an aura to a radius of 10-feet that captures creatures' shadows. Any creature within the area that casts a shadow must succeed on a Will save or become tethered to the ghost-stone via its shadow. The save DC is Charisma-based. A ghost-stone's shadowtrap aura does not function in areas of total darkness.
A creature trapped by the aura may not physically move outside the aura's area (or be physically moved by others), but is otherwise unhindered. A trapped creature can use teleportation or other forms of extraplanar escape to leave the shadowtrap area if they succeed at a caster level check (DC X plus the ghost's Hit Dice); otherwise they are affected as if by dimensional anchor. A consecrate spell cast within the shadowtrap area will temporarily disrupts the aura, granting trapped creatures one round to escape the aura. A creature with the shadow jump ability or other mode of shadow travel (such as the shadow walk spell) may escape the area as normal for the spell or ability.
At the end of its turn each round, a ghost-stone drains blood from each creature caught by its shadowtrap aura, doing 1d4? Con damage to each. Each time it drains blood, the ghost-stone gains 5 temporary hit points.
I can go along with dropping the hallow but I prefer the single-attempt teleportation, based on the
planar binding spell. Why, I was being kind allowing
one chance to escape.
Oh well, I would happier going along with multiple attempts if they got progressively more difficult (maybe a +1 DC per repeated attempt?).
I'd also fancy allowing clerics to "turn" the aura, something like:
A cleric can turn or rebuke the shadowtrap aura as if it were an undead creature with Y hit dice; a successful turn check temporarily disrupts the aura, granting trapped creatures one round to escape the aura. A consecrate spell cast within the shadowtrap area will also temporarily disrupts the aura for 1 round per caster level.
Oh, and as for the blood drain damage I was thinking of something pretty low. I was thinking we could make it 1d3 points per round or even just 1 point. It'd give the PCs a bit more chance to find a way to escape.
Anyhow, putting all that together...
Shadowtrap Aura (Su): A ghost-stone continually projects an aura to a radius of 10-feet that captures creatures' shadows. Any creature within the area that casts a shadow must succeed on a Will save or become tethered to the ghost-stone via its shadow. The save DC is Charisma-based. A ghost-stone's shadowtrap aura does not function in areas of total darkness.
A creature trapped by the aura may not physically move outside the aura's area (or be physically moved by others), but is otherwise unhindered. The shadowtrap area is under an effect similar to
dimensional anchor, a trapped creature must succeed at a caster level check to escape via
plane shift,
teleport or other forms of extraplanar travel (DC 10 plus the ghost-stone's Hit Dice plus 1 per additional attempt). A cleric can turn or rebuke the shadowtrap aura as if it were an undead creature with Y hit dice; a successful turn check temporarily disrupts the aura, granting trapped creatures one round to escape the aura. A
consecrate spell cast within the shadowtrap area will also temporarily disrupts the aura for 1 round per caster level. A creature with the shadow jump ability or other mode of shadow travel (such as the
shadow walk spell) may escape the area as normal for the spell or ability.
At the end of its turn each round, a ghost-stone drains blood from each creature caught by its shadowtrap aura, doing 1d3 Con damage to each. Each time it drains blood, the ghost-stone gains 5 temporary hit points.