Thillis' Monster Servant
(Charm)

Range:  5 feet per level
Components:  V, S
Duration:  Special
Casting Time:  2 rounds
Area of Effect:  One creature
Saving Throw:  Negates

Monster servant binds a creature to the caster's will. The spell does not grant any form of communication, so the wizard and the monster must be able to communicate for the spell to work. All humans, demi-humans, and creatures with an Intelligence greater than 10 are immune to the effects of the spell. Wisdom bonuses to saving throws apply if the monster actually has Wisdom.
An affected creature will do anything for the caster, including sacrificing its life. The spell's duration is similar to that of charm person, but the DM should modify this as he wishes. When the creature is told to place itself at risk, a new saving throw should be rolled.
But now for the fun part: this obviously overpowered spell has a mayor drawback: whenever the spell is cast, there is a chance, equal to (the target's Hit Dice - the caster's Wisdom bonus) divided by 20, that the spell drives the caster insane, and also subjects him to the creature's will at that point in time. Note that the spell still functions normally as well, so if the creature was wishing that the caster would be his slave, and the caster went insane, but the creature failed its saving throw, they would both be each other's slave.
Also, keep in mind that a caster with an 18 Wisdom could cast this spell on creatures of up to 4 HD, and as his Wisdom bonus is 4, there would be no chance of insanity.
This curse was not built into the spell, but was a side effect. The wizard that researched it did not put in a limitation on the target's Hit Dice, and drew the energy to enslave the creature from her own will power. Therefore, when she tried it on a creature of 14 HD, she didn't have the willpower to overcome it, and went crazy. Actually, she became its mate, thinking she was a fire giant. That's what the creature was looking for when she cast the spell...

