The final Horseman (or Horsewoman?) is Fury, she needs to be playable!
Each Darksiders game has one main protagonist, but maybe Darksiders 3 can have two? Where at the beginning of the game you pick who you want to play as, and the story unfolds slightly differently, why not have Strife and Fury playable in the same game. Then in Darksiders 4 you can play as any of the horsemen.
Fury wields a whip as her main weapon and claws for secondary. Not much is known about her personality, but she appears to be calmest of the Horsemen.
As Fury is level headed she could have an 'at peace' meter, as it fills up it will allow Fury to transform into something else, like with Death's Reaper form, she can then do higher damage, but also move a lot faster. Fury should be a very fast character using her agility do acrobatic attacks, and even some stealth, which, of course, will mean we need better AI and it MUST be optional --no forced stealth and no 'if detected you instantly fail' sections.
With the whip, Fury is then able to pull people from higher, or lower, places and maybe use it Indiana Jones style for swinging. Fury should have a much faster gameplay style, think more like Prince of Persia --Warrior Within specifically.