You cause a distortion in the timeline, reshaping the events of reality around you.

You undo a single recent event by forcing a reroll of any roll made within the last round (including your last turn). Reality reshapes itself to accommodate the new result. The DM has the final say on how reality reshapes itself. For example, you could undo an opponent's successful save, a foe's critical hit, or a friend's failed save. You can force the reroll to be made with Advantage or Disadvantage, and you can choose whether to use the reroll or the original roll.

Alternatively, you can attempt to distort the timeline in a stronger way, by negating a single action that was taken by a creature within the last round (including your last turn). Reality reshapes itself to accommodate the new result. The DM has the final say on how reality reshapes itself. For example, you could negate an Arcanist using Counterspell on one of your party's healing spells that would have saved your ally, or you could negate a dragon's breath weapon attack, thus preventing your ally from dying.

Using Time Regression in this way forces you to make a DC 20 CHA saving throw after the effect takes place. On a failed save, you gain one level of

Exhaustion

Whichever distortion effect you choose, select any number of creatures that you can see. These creatures, along with yourself, retain knowledge of the previous timeline. All other creatures within 100m must succeed on a WIS saving throw in order to retain this knowledge.