Agent Kallus: unlocked from Card Packs
Boba Fett: unlocked by completing mission 2
Bossk: unlocked by default
Darth Vader: unlocked by completing mission 7
Dengar: unlocked by completing mission 4
Director Orson Krennic: unlocked from Card Packs
Emperor Plapatine: unlocked by default
Grand Admiral Thrawn: unlocked from Card Packs
Grand Moff Tarkin: unlocked by completing mission 9
The Grand Inquisitor: unlocked from Card Packs