Time Dagger

Time Daggers are made from Time Dragon's teeth. Time Daggers are nasty business. They prune what they hit from existence. 

Time Daggers have been seen in Faerun by Toes Anonymous and in Elleswhere by the Lichen Morells Campaign party.

A Time Dagger in the hands of a Time Dragon will erase whatever it cuts from existence. A Time Dagger in any other Dragon's hand can erase, trim, and change whatever it cut's memories. It can prune what we want for you to remember. 

Mechanics-wise, Time Daggers would give a party-member advantage/disadvantage.