While The Mandalorian initially appeared to be laying the groundwork for a story exploring the creation of Supreme Leader Snoke, the series has also set the stage for Grand Admiral Thrawn to make his return.
The villain was last seen being pulled through hyperspace alongside Ezra Bridger in Star Wars Rebels, though no one knows where the ancient Purrgil took them. Ahsoka Tano is searching for Thrawn, though, and believes that, by finding him, she'll be reunited with her old friend.
According to Making Star Wars (via SFFGazette.com), aiding Morgan Elsbeth in her mission to find Thrawn are two characters named Baylon and, his apprentice, Shin.
Ray Stevenson plays Baylon and is thought to be a former Jedi who escaped Order 66. However, he's fallen to the Dark Side and allegedly has a storied history with Thrawn (the site speculates that the Imperial may have saved him from death or being turned into a Sith Inquisitor, thereby creating a bond of sorts between the two men).
His armour has some "samurai aesthetics," while his weapon is described as a "red claymore saber" that's heavier than then norm and swung with immense power.
Shin (played by Ivanna Sakhno) is the one who supposedly leads a squadron of undead Stormtroopers against Ahsoka and our heroes later in the series. As the site explains, their helmets have "red and gold filament that moves along the fine veiny cracks," while they also boast "magic red bands tied around various parts of their armor that were put there by the Nighsisters."
As for Shin's weapon of choice, that's a "'red rapier lightsaber' and she moves lightning fast with the blade."
It's become clear that Ahsoka is going to explore the Force and the Star Wars mythos in ways unlike anything we've seen before, though that lines up with much of what we saw in Rebels. How this will inform the story Jon Favreau is telling is hard to say right now, though we have all the faith in the Galaxy in Dave Filoni...