Well, this is my own DC set that runs along with FM's block. I don't have a really long, in-depth storyline made up, but by the end of FM's third set (when this set takes place) his five planeswalkers have forged alliances (between allied colors, of course) and have mostly settled on a structure for their new world. However, my set depicts the "duplicity" of the planeswalkers - they will double-cross one another at any chance they get and forge alliances against one another, with the end goal still being the greatest power over this new world.
So, I'm thinking that the things that will be prevalent in this set are enemy color combination, as well as single colors, and a bit of multicolor hate.
I'll throw out a few spoilers.
Light of Lyn 1
Instant
Chroma - You may tap a target creature for each white mana symbol among the costs of permanents you control.
All the world would fall to its knees before Lyn's divinity.Knowledge of Abel Instant
Chroma - Counter target spell unless its controller pays (1) for each blue mana symbol among the costs of permanents you control.
All the world would cower before the mind of Abel.Ambition of Baal Instant
Chroma - Target creature gets -1/-1 for each black mana symbol among the costs of permanents you control.
All the world would fall victim to the shadow of Baal.Rage of Morwen Instant
Chroma - The Rage of Morwen deals 1 damage to target creature or player for each red mana symbol among the costs of permanents you control.
All the world will burn in the anger of Morwen.Ferocity of Aalistair 1
Sorcery
Chroma - Put an X/X green Beast creature token with
trample into play, where X is the number of green mana symbols among the costs of permanents you control.
The world will be beaten to dust by the strength of Aalistair.