I would like to join the chosen undead club. After seeing how Sakurai design Steve moveset, I think thay can do justice to Chosen Undead. Dark Souls and Minecraft are the most influential games of the decade, and although I’m not a 100% fan of Dark Souls but I would not be mad if they chose him as a future DLC fighter.
As some have said, I agreed that they should include an stamina bar, the parry technique and etus flask (5 per stock, no refill like Banjo-Kazooie gold wings). Considering they are various classes in DS that focuses on different things, I think that Smash team would focus on the universal features of the souls trilogy. That gets me to imagine Chosen Undead as a sword and shield fighter, who can change from one-hand sword to two-hand user, dealing more damage but decreasing its defense.
The default alt is the elite knight set, then as alternative you would have faaram and firelink armor set (+ one different color variation for each of them). They are the most iconic armor set of each Souls game. Each armor would also have their own sword and shield (like Hero).
Just like Steve, the final 2 alts would have different names, one is Solaire of Astoria (iconic NPC, it even has its own Amiibo) and Black Knight (important DS enemy, plus, the Dark Knight figure is common and popular in medieval settings like FE games).
As the stage, I choose Firelink Shrine based on the first game, its one of the first places you visit and most known by general public. Just like Mementos, depending on the music, the background color will change and like KOF Stadium, different NPCs will appear at the background.
For music, put different bosses songs, 3/4 from each title.