A scientist is killed by Grodd after stealing some chemicals from a lab and Joe and Patty investigate in episode 2x07 "Gorilla Warfare".
Wally tries to stop a purse snatcher only to realize he is up against a meta-human in episode 2x22 "Invincible".
Barry and Iris see a broadcast about the battle between Kid Flash and The Rival while at Jitters in episode 3x01 "Flashpoint".
Barry follows Cisco to the gym and finds him attending a support group in episode 3x02 "Paradox".
Lucious Coolidge AKA Heat Monger walks into an office and lights it on fire with his flamethrower in episode 3x21 "Cause and Effect".
Barry examines the mug he stole from Clifford DeVoe's desk in episode 4x07 "Therefore I Am".
Clifford DeVoe gets a diagnosis from a doctor in episode 4x07 "Therefore I Am".