Here is a very simple chart for throwing a curve to the monsters / foes in DnD that your party will face. Roll D4 - 1 for number of changes for each group of monsters/foes encountered. Then roll a D12 on the chart below for each change. 1) Increased HD (1-2) 2) Attack more damaging (one die up) 3) New Magical ability (per spell of HD - 3, min level 1 mage or cleric power) 4) Additional Feat or feat like power 5) Increased (better AC) 6) Additional Attack 7) Increased number of appearing 8) Unlikely ally monster(s) of 1-2 less 3-4 equal or 5-6 greater strength 9) Alignment / motivation change (sometimes beneficial) 10) Reinforcements near by 11) Treasure type increased by one letter (or equivalent) 12) Monsters / Foe more cunning that usual (ambush, traps, delays)