Quicksand! like depth 2 water, only sand.
Seriously though, how crazy are you able to get? What about adding status effects (like the swamp poison) or straight damage/healing? I was thinking like a plant or sacred ground that would heal you every turn you start on it, or spiderwebs that cause slow, or panels that boost certain damage types like weather effects do (snow boosts ice, wood or dry brush boosts fire, etc)
Seriously though, how crazy are you able to get? What about adding status effects (like the swamp poison) or straight damage/healing? I was thinking like a plant or sacred ground that would heal you every turn you start on it, or spiderwebs that cause slow, or panels that boost certain damage types like weather effects do (snow boosts ice, wood or dry brush boosts fire, etc)