Elemental Isle Nihl
Tired of your players always stomping on around bare unmarked grassland? Well my friends that grass is not always greener.
After players spend enough time in terrain they become adapted to it and no longer need to worry about any failure by 10 clauses. Normally it takes 10 battles but the number is reduced by either your Intelligence or Wisdom.
Nothing ruins an acrobats day like being knee deep in mud. Arbitrarily designate a few spots as mud and only a high nature check (not perception) will allow a player to be able to tell their location. Once they enter it they plunge down and require a successful Athletics check to free themselves.
Nothing is as treacherous as swinging hefty weapons on the uncertain footing provided by your friendly local desert. When making an attack or charging have you players make acrobatics check. If they fail their swing goes wild and they take a -5 penalty to attack. If they fail by 10 or more they fall prone after the attack. If they somehow fail by 20 or more have them fall on their asses at the start of the action and do nothing else for the turn.
Watch out for low hanging branches! Whenever players move 2 squares through difficult terrain there is a chance they get hit by low hanging branches or plow through some prickly underbrush. They take an automatic d8 or 2d8 of damage reduced by armor as normal.
Athletics or Acrobatics check to avoid being slowed at the start of the round. Anyone in medium armor takes an extra -1 to speed and heavy armor takes an extra -2 speed. Yes that’s right, people in Plate mail have the chance to move zero squares in a turn. DUN DUN DUN.
Whenever a player moves at least 3 squares they must make an acrobatics check. Failure by 5 or more causes them to slide a square or two, failure by 10 or more causes they to slip and fall prone.