Young Justice Invasion S02 E06

A stranger appears within Mount Justice claiming to be a time traveler and the grandson of the current Flash. The boy, Bart Allen, soon escapes and gatecrashes the celebration of the Garricks' wedding anniversary, revealing his identity to Barry Allen and Iris. The party is interrupted when they all learn that a villain called Neutron is on a rampage downtown, and the Flash Family head off to stop him. Meanwhile, Red Arrow and Cheshire travel to a League of Shadows base in Tibet, and there they find the original Roy Harper.
In Central City, the Flashes defeat Neutron and Bart, having taken the name Impulse, secretly administers something that cures Neutron. Later, Impulse says his goodbyes, only to find that his time machine is broken and that he is stranded in the present day.