Alie and Jaha talk in the City of Light in episode 3x02 "Wanheda: Part 2". Alie tells Jaha that Raven knows how to destroy her in episode 3x11 "Nevermore". Jaha and Alie use Monty's mother to slow Raven's attack in episode 3x14 "Red Sky at Morning".
The Trickster poisons people at the Mayor's press conference that Iris is attending in episode 1x17 "Tricksters".
Cassandra trains with some soldiers before being kidnapped by Snart and Rory in episode 1x13 "Leviathan".
Source: VanFlarrowFan — Twitter
Kiera arrives in the future at the feet of Kagame and is then greeted by future-Alec in episode 4x06 "Final Hour".
Cyborg Superman breaks into the lobby of L Corp to steal the isotope needed to use the Medusa virus but is thwarted by Kara in episode 2x08 "Medusa".
Source: What's Filming
Lyra takes Winn to the art gallery and convinces him that they should break in to have some hot museum sex in episode 2x16 "Star-Crossed".