1x18 Worlds Finest
First Aired: Mar. 28, 2016 on The CW
Summary: Kara gains a new ally when the lightning-fast superhero The Flash (guest star Grant Gustin) 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.
Guest Stars[no credits found]