Halbrand is Galadriel’s bestie in Season 1. The two meet on the high seas, where Halbrand immediately begins getting under Galadriel’s skin. Slowly, her distrust is compromised … until, hey presto! Her new best bud reveals himself to be Sauron in disguise. The Elf rejects the Dark Lord’s offer of power, leading to Halbrand’s rapid withdrawal from the situation.
While he does hightail it back to Mordor, there’s certainly potential that Sauron could come back in Season 2 in a new way. In fact, some leaks have already hinted that he could be showing up in a different form. (He’s a shapeshifter, so he can do that kind of thing.)
If that happens, we might end up seeing a different version of the Dark Lord. He might even show up in his infamous form of “Annatar, the Lord of Gifts.” This is a hidden persona (like the Halbrand one) in which Sauron pretends to help the Elves make the Rings of Power. Since JD Payne and Patrick McKay’s show has opted to only make the Three Elven Rings so far (a significant deviation from J. R. R. Tolkien’s ring-making timeline, where they’re made after the Rings for Men and Dwarves), it’s entirely possible that Sauron will secretly come back in the form of Annatar to help make the rest of the overpowered trinkets.