Carry out flash missions and win Lianah Ld !
Lianah Ld is a legendary character who is only available by carrying out missions connected with it. To obtain this character, you must complete its last mission before the 02/10/2016 (2 October 2016)
They already changed the order and jumped to an LD not available from Arcade so really, your guess is as good as anyone's.
I'm gonna say Jaxx Ld, just because nothing's more fun than trying to get ability effects against a SoA clan.