Play a cards that can buff a unit repeatedly and some units that are good with buffs. Follow the standard "play small units and buff them" plan, but the buff comes from a bunch of small abilities instead a single source, so it's harder to get rid of. Set up boards with lots of buff abilities so you can spend power on those rather than the cards you draw. Then use those cards to protect and refill the board as they try to deal with it. Been having decent success at rank 500-300 Masters.