A lot of your most impactful cards are going to be in the 3, 4, and even 5 or more cost range, so you'll be laying a lot of hopes on individual characters here (as opposed to building up a wall of characters as in the Amber and Amethyst deck)
Which scene is your favorite so far
So getting 2 or maybe 3 Lore out of her when she Quests would be worth having her on the list
No Liliana of the Veil or Snapcaster Mage in sight, but I would be shocked if they weren't in the set.
Practice, Practice, Practice One of the things I would do when making the challenges for CCC is to make 5-7 cards per prompt, preferably one per color and a colorless where applicable
Only playable in a select few formats, Brainstorm's strength lies in the sheer amount of card selection it gives you