Though it's still technically set in another universe (for), it looks like CW's Supergirl will crossover with the rest of the CW-verse more often than first expected. In addition to the four-way DC's Legends of Tomorrow/Flash/Arrow/Supergirl crossover already planned for November, Flash and Supergirl will join forces for a two-part musical episode.
This move isn't that surprising considering Flash star Grant Gustin and Supergirl star Melissa Benoist are both Glee alumni, and the question of a musical episode has been a frequent one. The episode was announced by Greg Berlanti at a Television Critics Association event (via Deadline).
Additionally, Supergirl, Arrow, Flash, and DC's Legends of Tomorrow are all gaining new castmembers.
Flash season 3 will feature a visit from Savitar, a Flash enemy and evil superspeedster from the 90's.
On the flipside, it looks like Supergirl may be gaining a pair of alien allies in the form of Miss Martian (played by Sharon Leal) and Mon-El (played by Christopher Wood.)
This would be the first live action appearance for all three characters. Though not much is known about Savitar or Miss Martian's TV origins, Mon-El will be a Daxamite with similar powers to Supergirl who was a visitor to Krypton prior to its destruction.
Over on Arrow, genre favorite Dolph Lundgren will join the cast in an unnamed role, appearing in flashbacks taking place in Russia, while Lance Henriksen joins DC's Legends of Tomorrow, also in an unnamed role.
The Flash's new season on the CW begins October 4, followed by Arrow on October 5. Supergirl will follow on October 10, rounded out by DC's Legends of Tomorrow on October 13.