A Zen Stone is named after Zen, a chronurgy wizard who posses great knowledge and even prophecies of events to be aware of. Many types of Zen Stone exist, each type a distinct combination of shape and color, and usually created by Zen for a very specific character to hold for their lifetime in order to influence the timeline in a subtle way. Though there are so many of them that it isn't unheard of for an unintended person to have possession of one.

ZEN'S STONES: All of Zen's stones have the ability to be used to create a chronal shift with one charge that recharges after a long rest, and this does not require attunement, you merely have to have the stone in your posession. To use this ability you use a reaction and speak the words Chronos Maniputale and you can magically exert limited control over the flow of time around a creature. After you or a creature you can see within 30 feet of you makes an attack roll, an ability check, or a saving throw, you can force the creature to reroll. You make this decision after you see whether the roll succeeds or fails. The target must use the result of the second roll.

ATTUNEMENT: Once attuned to this item you can use an action to toss it in the air and it will hover 3 ft above your head granting you a special gift as long as it does so.

A stone has AC 24, 10 hit points, and resistance to all damage. It is considered to be an object that is being worn while it orbits your head.  If it ever has 0 hit points it falls to the ground and appears to be a normal stone.  It is no longer attuned to you.  It will regain it's hit points and all it's power when you take a long rest and you may attune to it again during that long rest. 

Leadership. Your Charisma score increases by 2, to a maximum of 20, while this marbled pink and green sphere orbits your head.

Notes: Bonus: Charisma Score, Buff