What are the requirements for emperor palpatine event

To unlock, 5 x 5* rebels. To get 6*, 5 x 6* rebels etc.

Just found this handy thread that I didn't know existed containing the requirements for all events:
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/154696/reoccurring-events-and-characters-required-index

Also try and put a decent team of rebels together. While 5 random rebels will get you in the event, decent synergy is needed to actually beat it.

Ackbar tactical advantage plus decent speed Lando. Killed Vader and 1 Royal Guard with Lando's 2 Double Downs. Taunted to sacrifice ST Han. Biggs killed the next Royal Guard with his Comrade-in-Arms. Then four left to waste Palpatine with a cleanse or two from Ackbar to regenerate health.

Thanks you guys so much!!!