This spell is similar to the 9th-level wizard spell time stop. When reverse time is cast, time stops within a 30-foot diameter of the subject. All creatures and items in the area of effect stand motionless, rivers stop running, and arrows hang suspended in the air. Any creature, person, or object entering the area of effect is likewise frozen in time. The caster is affected if he is within the area of effect, unless he is the subject of the spell.
An unwilling subject is allowed a saving throw vs. spell; if successful, the spell is immediately negated. Otherwise, the victim is forced to relive all the actions taken in the previous 1-4 rounds in reverse. Beginning with the most recent round, the subject moves backward, arrows fired by the subject return to his bow, and so on. All effects of these actions are negated. At the end of the spell's duration, normal time resumes and all creatures immediately continue their activities, picking up right where they had stopped.
Consider the following example. A party is battling a spellcasting red dragon. In the first round, the dragon breathes fire, roasting the party's wizard. The rest of the group attacks and injures the dragon. On the second round, the dragon bites and kills the group's thief. More damage is caused to the beast, but it is still alive in the third round, when it uses magic missile to kill the ranger. At this point, the priest casts reverse time on the beast. Fortunately, it fails its saving throw and is forced to reverse the last four rounds.
While everyone else freezes, the dragon goes into reverse. The magic missiles zoom back to the dragon (and it regains the ability to cast that spell), it "unbites" the thief (removing that damage from the character), and then inhales its fiery breath (leaving the roasted wizard alive and uncooked). The dragon is then reversed through one more round—the round before it encounterd the party. The spell then ends and actions resume.
The dragon must now roll for surprise since it is encountering the party for the first time. The party is immune to surprise, since it was fighting the beast previously. All damage suffered by the dragon remains, since these actions were caused by the group and not the beast.
The material component is an etched silver arrow bent into a circle. The arrow must be no more than 3 inches long and worth no less than 500 gp. The arrow is destroyed in the casting.