Ryujin
Legend
And they already introduced and subsequently screwed up The Justice Society, in "Black Adam", so there's no quick Earth 2 reboot potential.Not really, because they did Crisis on the TV shows and Ezra appeared on that (as a prequel to this, I guess), meaning that counts as the cinematic universe's Crisis.
This being DC, though, they have two crises a day, one before breakfast, so there's plenty to go around.