This is awesome. Heroic Hollywood has the poster and episode description for the March 28 crossover episode of Supergirl featuring Grant Gustin as The Flash.
“Worlds Finest” – Kara gains a new ally when the lightning-fast superhero The Flash (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, on SUPERGIRL, Monday, March 28 (8:00-9:00 PM) on the CBS Television Network. Grant Gustin crosses over as The Flash.
Supergirl stars Melissa Benoist (Kara Danvers/Supergirl), Calista Flockhart (Cat Grant), Chyler Leigh (Alex Danvers), Mehcad Brooks (James Olsen), David Harewood (Hank Henshaw/J’onn J’onzz), and Jeremy Jordan (Winslow “Winn” Schott).
Recurring guests in “Worlds Finest” include Jenna Dewan-Tatum (Lucy Lane), Chris Vance (Non), Italia Ricci (Siobhan Smythe), Brit Morgan (Leslie Willis/Livewire), Christopher Showerman (Tor), Jay Jackson (News Anchor), and Dan Warner (Fire Captain).
Guest stars in the episode also include Grant Gustin (The Flash/Barry Allen), Jamie Kaler (Pundit #1), Samantha Harris (Pundit #2), Zarek King (Young Boy), Sarah Robson (Dr. Amelia Hamilton), Harriet Sansom Harris (Sinead), Dawn Greenidge (Pedestrian Woman)
STORY BY: Greg Berlanti
TELEPLAY BY: Andrew Kreisberg & Michael Grassi
BASED ON: The Characters Appearing in the DC Comics
DIRECTED BY: Nick Gomez.