You can sicken creatures with your songs.
You can modify a song to sicken a creature damaged by the song. When a creature takes damage from this song, they become sickened for a number of rounds equal to the original level of the song. If the song allows a saving throw, a successful save negates the sickening effect. If the song does not allow a save, the target can make a Fortitude save to negate the sickening effect. If the song effect also causes the creature to become sickened, the duration of this metasong effect is added on to the duration of the song. Songs that do not inflict damage do not benefit from this feat.
MP Increase: +2 (a sickening song costs 2 additional MP more than the actual MP cost of the song.) In addition, the perform check DC increases by +2.