Tuesday, October 8th
The cancelled Mewtwo raid day that had originally been set for September 18 has been confirmed via a tweet by Niantic to be rescheduled for Tuesday, October 8th from 6:00 pm to 7:00 pm local time.
Trainers, the make-up Legendary Raid Hour featuring Mewtwo with the move Psystrike will be on October 8, 2019 from 6 p.m. to 7 p.m. local time. Stay tuned for details.
— Niantic Support (@NianticHelp) September 20, 2019
Related Mewtwo Content
For more info about Legendary Raid Hour Mewtwo, check out the following guides below.