Something simple to shake things up a bit: tile/s, like a chasm or pit, that instantly kill any character occupying them at the start of each round. Getting pushed onto the chasm tiles means nothing mid-round, rather it represents the back-and-forth efforts of characters to either push something into the chasm, or prevent themselves being pushed. You'd introduce it to a campaign map - imagine something like the AI cake boss where you're flinging its spawned slice creeps into a 1 x say 6 chasm (so too narrow to fling the boss itself into). However, imagine the specialised builds that would have to deal with something like this on a regular MP map. Suddenly, cards like immovable, hover, vanguard, entangling roots, purge, step attacks, hypnotic beacon, arrogant and the various control cards become critical, and the balance becomes "Will I take low damage defensive/offensive control cards, or will I load up on high damage cards and risk having my characters pushed into the chasm?" It may change how some cards work: would nimbus prevent you from death by falling (maybe not), would dim traveller allow you to skip out of the chasm at the start of the turn (maybe), etc.