This currently serves as the final story arc of the series unless Season 3 happens.
The saga started in "The Greater Hater," with Lord Hater falling low on the level of cosmic threat, which is when Lord Dominator, supposedly a far better villain than Hater himself, makes their appearance.
The second episode in the saga, "The Battle Royale", reveals to the other characters that Dominator is a woman, having been found out by Wander, who tries to pair her up with Hater. However, not only does the matchmaking attempt cause a huge battle between the galaxy's villains and Dominator, but it only works for Hater, who falls in love with his new nemesis.
The penultimate episode, "My Fair Hatey", had Dominator's true plan be revealed as the absolute destruction of the current galaxy. Also, Hater and Wander finally get the hint she's nothing like what they expected, and in a failed attempt to get rid of her for good, she obtains ice powers alongside her lava powers. Seeing their mistake, Wander, Hater, Sylvia, and Peepers decide to save the galaxy.
The final episode of the Lord Dominator Saga and the whole Wander Over Yonder series altogether, "The End of the Galaxy", has Wander, Sylvia, Hater, and Peepers save the last surviving planet from being destroyed by Lord Dominator. After a failed attempt to destroy the planet, Dominator gets defeated.