Casting this spell attempts a dangerous act: to lure a powerful creature from another plane to a specifically prepared trap, where it will be held until it agrees to perform one service in return for freedom from the ensnarement spell. The type of creature to be ensnared must be known and stated, and if it has a specific, proper, or given name, this
must be used in casting the ensnarement spell. The spell causes an awareness of a gatelike opening on the plane of the creature to be ensnared. A special saving throw is then made to determine if the creature detects the nature of the planar opening as a trap or believes it to be a gate. To save, the creature must roll equal to or less than its Intelligence score on 1d20. The score is modified by the difference between the creature's Intelligence
and that of the spellcaster. If the creature has a higher score, the difference is subtracted from its dice roll to save. If the spellcaster has a higher score, the difference is added to the dice roll.
If the saving throw succeeds, the creature ignores the spell-created opening, and the spell fails. If the saving throw fails, the creature steps into the opening and is ensnared.
When so trapped, the otherplanar creature can freely attack the ensnaring wizard, unless the caster has created a warding circle. Such circles may be temporary (drawn by hand) or permanent (inlaid or carved). Even with such protection, the entrapped creature may break free and wreak its vengeance upon the spellcaster.
A hand-drawn circle has a base failure chance of 20%, while one inlaid or carved has a base of 10% (and that is for the first time it is used, to determine whether or not the job was done properly). The base chance is modified by the difference between the wizard's combined Intelligence and experience level and the Intelligence and the experience level
or Hit Dice of the creature ensnared. If the spellcaster has a higher total, that difference in percentage points is subtracted from the chance for the creature to break free. If the creature has a higher total, that difference is added to its chance to break free.
The chance can be further reduced by careful preparation of the circle. If the handmade circle is drawn over a longer period of time, using specially prepared pigments (1,000 gp value per turn spent drawing), the chance of breaking free is reduced by 1% for every turn spent in preparation. This can bring the base chance to 0%.
Similarly, an inlaid or carved design can be brought to a 0% chance of the creature breaking free by inlaying with various metals, minerals, etc. This cost will require a minimum of one full month of time and add not less than 50,000 gp to the basic cost of having the circle inlaid or carved into stone. Any break in the circle spoils the efficacy of
the spell and enables the creature to break free automatically. Even a straw dropped across the line of a magic circle destroys its power. Fortunately, the creature within cannot so much as place a straw upon any portion of the inscribed ward, for the magic of the barrier absolutely prevents it.
Once safely ensnared, the creature can be kept for as long as the spellcaster dares. (Remember the danger of something breaking the ward!) The creature cannot leave the circle, nor can any of its attacks or powers penetrate the barrier. The caster can offer bribes, use promises, or make threats in order to exact one service from the captive creature.
The DM will then assign a value to what the wizard has said to the ensnared creature, rating it from 0 to 6 (with 6 being the most persuasive). This rating is then subtracted from the Intelligence score of the creature. If the creature rolls a successful Intelligence check against its adjusted Intelligence, it refuses service. New offers, bribes, etc., can be made, or the old ones re-offered 24 hours later, when the creature's Intelligence has dropped by 1 point due to confinement. This can be repeated until the creature promises to serve, until it breaks free, or until the caster decides to get rid of it by means of some riddance spell. Impossible demands or unreasonable commands are never agreed to.
Once the single service is completed, the creature need only so inform the spellcaster to be instantly sent from whence it came. The creature might later seek revenge.