Iris tries to use Barry's wind funnel trick to put out the fire but only makes things worse in episode 4x16 "Run, Iris, Run".
Nora and Barry arrive to stop a fire at the news studio but Spencer Young uses her powers to draw Barry away forcing Nora to stop the fire on her own in episode 5x04 "News Flash".
Lucifer shows up at the police station to meet with Lt. Monroe in episode 1x05 "Sweet Kicks". Chloe and Dan talk about the Palmetto case in episode 1x07 "Wingman". Malcolm talks to Dan in episode 1x09 "A Priest Walks Into a Bar". Appears in 2 more episodes.
Source: YVRShoots — Twitter
Oliver and Sara fight Count Vertigo on a rooftop across the the boxing arena in episode 3x01 "The Calm".
Team Arrow battles Derek Sampson and his goons to stop the release of a deadly virus in episode 5x21 "Honor Thy Fathers".
Thea zip-lines over to the hotel where Roy is being held and sneaks inside while the police officers are distracted by fireworks in episode 6x15 "Doppelgänger".
Zimmerfield & Estevez discuss the incident at the hotel and Todd in episode 1x01 "Horizons". Todd comes in to talk about seeing Lydia Spring in episode 1x03 "Rogue Wall Enthusiasts". Zimmerfield gets suspicious of the replaced Agent Weedle when he comes by asking questions in episode 1x04 "Watkin". Appears in 3 more episodes.
Webb is discovered injured after a battle with the Men of the Machine by his future wife in episode 1x07 "Weaponized Soul".