Supergirl - S01E18
Kara gains a new ally when the lightning-fast superhero The Flash suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home.
The Flash (2014) - S03E22
With only 24 hours left until Savitar murders Iris, Barry struggles to save the woman he loves and makes the choice to use any means necessary to do so. Realizing he has one option left to save her, The Flash turns to Captain Cold for help.
Arrow - S07E13
Oliver and Felicity are disappointed after they learn that William is hiding something from them. Wanting to focus on his family, Oliver steps back from his Green Arrow duties and lets the team take over tracking down a serial killer. However, when the team becomes targets for the killer, things take a bloody turn.