Master?s Wil( Elder Evils, p. 13)
The elder evil you serve is fickle in its rewards and punishments.
As an immediate action, you can beseech the elder evil for assistance. Roll 1d20. If the result of the die roll is an odd number, you gain a +8 bonus on one attack roll, saving throw, ability check, or skill check for 1 round. If the result is even, you take 1 point of damage for each Hit Die or character level you possess.
You must make the decision to use this ability before making an attack roll, save, or check.