Ghostblade - Has two main unique mechanics that I think will appear in Duel: his ghost partner and his Ghost Step stance.
Ghostblade is possessed by another spirit that follows him and can attack independently, sort of like a Stand. Ghostblade has several skills that send the ghost out to attack, or skills where he and the ghost attack in tandem. He can use a skill called Ghost Retracer to switch places with his ghost, allowing him to teleport around the stage.
Ghost Step is a command dash that lets him very quickly zoom around the fight while attacking. Activating Ghost Step puts him in a stance, and then attacking causes him to dash/teleport forward while slashing his sword. The gimmick is that if Ghostblade inputs any of his (non-ghost) specials while in the stance, then instead of attacking normally, he will dash and perform an enhanced version of that special instead. If Ghostblade is good about constantly cycling into Ghost Step stance, he has a lot more AoE, damage, and can remain constantly mobile.
Mechanic - Male Mechanic (who came first) is a kind of summoner archtype that is kinda comparable to Jack-O. He summons little robots that attack opponents automatically, and can also summon tiny factories that build more robots. Female Mechanic is the one appearing in Duel instead. She can summon robot hordes like that, but it isn't her focus. Instead, FMech is focused on a single transforming robot partner called the G-Series. G-Series usually floats around the Mechanic and can transform between a couple different types. G-1 is a mortar cannon that sits behind her and fires projectiles. G-2 is a set of orbiting options that create a damaging barrier in front of her. G-3 is an array of floating laser cannons that she can order to fly above an opponent and fire on them.
Troubleshooter - Bruce Willis: The Class. He's designed to be easy and beginner-friendly in DFO, so he does not have lots of special cancels or other complex mechanics. He uses a shotgun (in contrast with the Hitman's SMG) and also has lots of explosives. All of his attacks are big and loud and cover a wide area. He is not the fastest, so he has several attacks that hold/immobilize enemies, or knock them down, which gives him time to set up his bombs.