Baron Valen Rudor, likely for being a Mook with personality and being a Butt-Monkey. In fact, he's one of the first characters introduced, having been a main character in the Ezra's promotional short, "Property of Ezra Bridger".
Hondo Ohnaka retains his Ensemble Dark Horse status from the previous series.
The Seventh Sister, for her creepy interaction with Ezra. She gets talked about far more often than her male counterpart, the Fifth Brother. As the season went on however, many felt that she suffered from Villain Decay and didn't deliver as much as they expected.
Lt. Yogar Lyste got some respect when he came back in "A Princess on Lothal" as being one of the most competent Imperials shown onscreen, clearly wanting to do his job as well as he can despite any possible misgivings he has of anything, in comparison to most of the other officers that lost usually due to ego.
Kalani did not have this status back in The Clone Wars, but seems to be building up as one by virtue of being the super tactical droid leader of a Separatist holdout, Separatist droids and holdouts having been long awaited to see in the Rebel-Imperial Era.
Minister Tua had this status back in Season 1 (especially on Tumblr, for some reason, probably due to Moe; 4chan apparently thinks she's hot), and despite the short amount of screentime she had, her Wookieepedia page had considered nominating her page as a featured article and her voice actor was nominated for Best Female Vocal Performance in a Television Series in a Supporting Role – Action/Drama on IMDb.
When she was first seen in the preview for "Iron Squadron", many fell in love with Gooti's design, especially since she was the Token Non-Human in the group. Though after the episode aired, she seems to have fallen out of favor, though some agree her design is still great. Being a Shout-Out to Andi, the lovable host of Rebels Recon, certainly gives her brownie points as well.
Imperial Captain Brunson in "Ghost of Geonosis". Fans who mistaken her as Rae Sloane at first glance were not disappointed to learn that there was another visible Imperial woman of color given some prominence, notably the first one on-screen. Her professional rookie quirks helps.
Fenn Rau became one in Season 3 for his Mandalorian badassery and basically being Sabine's new space-uncle.
Pellaeon was a massive player from Legends, but he only has one line in the entire series. That doesn't stop fans from flooding Youtube and various media outlets from talking about him. Word of God is that he is alive, like Thrawn and Ezra, paving the way for future appearances within the series.
Jacen Syndulla for being the ultimate symbol of Kanera.
