Barry is attacked by the shark-man and is saved by Harrison Wells when Patty's gun is insufficient for the job in episode 2x04 "The Fury of Firestorm". The police fight against the meta-humans under Zoom's control in episode 2x22 "Invincible".
Cisco has a vision of birds crashing into the ground on Earth-2 in episode 2x22 "Invincible".
Cisco travels to Earth-19 where Cynthia Reynolds is reporting on the success of her latest assignment and tries to get her to return to help on Earth-1 in episode 3x14 "Attack on Central City".
Chloe and Lucifer approach John Bryant who is photographing some celebrity in episode 1x02 "Lucifer, Stay. Good Devil.".
Lucifer and Maze go to talk with the man in charge of Dr. Martin's ethics investigation in episode 2x17 "Sympathy for the Goddess".
Diggle follows Moira to a covert meeting with Malcolm and overhears part of it in episode 1x13 "Betrayal".
Oliver chases The Dodger though the streets in episode 1x15 "Dodger".
Laurel rants about her father spying on her to Tommy who gets mad about her talking to The Vigilante in episode 1x13 "Betrayal".
Diggle finds one of the virus carriers at a downtown plaza who is then taken out by Thea in episode 3x23 "My Name Is Oliver Queen".
Oliver meets Merlyn in a downtown square in episode 3x04 "The Magician".
Kendra and Carter part ways with the group and Oliver and his crew get ready to head back to Star City in episode 4x08 "Legends of Yesterday".