The Brothers War revisits the events of the Antiquities set and a brutal war between the brothers Mishra and Urza
Use spells like Raise the Alarm, Krenko's Command, and Hordeling Outburst to quickly build a massive army
I could very much see adding in Proteus Staff and some single target polymorph spells because it's really a lot of fun to pop a creature token and see what creature or creatures you can plop onto the battlefield
Some of these decks are loaded with artifacts, some crank out tokens like theres no tomorrow, and others mess with souls, shields, and even full-on orcs
There's no need to build around her, Belle is universal utility to be slapped into every Sapphire deck.
These three planeswalkers aren't particularly innovative, they just expand upon changes we'd already made: other versions of existing characters, narrower thematic focuses, etc