Noticing some design trends from new cards.
Modern Curser - Design a junking attack which is unlikely to put Curses into other players decks before the "mid game" - Idol, Black Cat, Sorcerer/ess, Coven, Cauldron, Witch's Hut, Siren, Trickster, Circle of Witches
Shuffle manager - Design a card that (explicitly or otherwise) is built around impacting your next shuffle (e.g. Avoid, Order of Masons, Prepare, Deliver, Coastal Haven, Grotto, Journey)
Innovation style - Design a card that can be played in reaction to a Gain (e.g. Sheepdog, Stowaway, Pirate, Trail) or allows other cards to be (e.g. Innovation, Sailor, Mining Road)
Power $4s/Timmy $4s - Design a card that is potentially very strong, but not a particularly good opener (e.g. Tools, Swamp Shacks, I guess Throne Room also counts) and so costs less than $5
Bend the Rulebook - Design a card that encourages players to better understand more obscure rules (e.g. Siren and the stop moving rule)