I just really like how ArcSys likes to shake things up when it comes to gameplay mechanics for new characters.
From what we know Jack-O has a bunch of Dust specials (some consume some meter apparently), a strike throw that can end aerial combos in Melty Blood fashion.
Can summon pumpkins onto the stage that level up over time which can then summon strong minions presumably (3 different kinds from what has been shown so far). These pumpkins can also be picked up and moved around/thrown. And we still don't know what her HS special does or any of her supers (and her Instant Kill is currently unfinished and not usable).
Already what's there is pretty intriguing, they only thing I can think of that's vaguely comparable is maybe Zappa's ghost summon (different types but can only have one type active at a time).
I think their strategy of introducing pairs of one old and one new character is a good one. The old roster can be brought back up while they also introduce newcomers at the same time.