Critical Hits:
If you roll an unmodified natural 20 on your attack roll you score a critical hit. Roll damage twice and add the results, modifiers to damage such as from high Strength are only counted once. If you roll max damage on any of the damage dice roll again and add those results to the total.
Example: Bob the Third scores a critical hit with his shortsword. He rolls 2d6 for damage and gets 3 and 6 on the dice. Seeing as he rolled max on one die he rolls 1d6 again to add to the total, he rolls 4. Bob adds all the dice together and ends up dealing 13 damage plus whatever modifiers he normally adds.
Critical Fumbles:
If you roll and unmodified natural 1 on your attack roll you critically fumble your attack. When you fumble any enemies within melee range may make an immediate melee attack against you.
Bloodied and Wounded:
All characters have a bloodied and wounded score that is determined by hit points. A characters bloodied value is equal to ½ their total hit points and their wounded value is equal to ¼ their total hit points. Whenever a character is reduced to their bloodied score or lower in hit points they take a -2 penalty on all d20 rolls until they are healed to above their bloodied value. Likewise whenever a character is reduced to below their wounded value they take a -4 penalty on all d20 rolls (does not stack with bloodied penalty) until they are healed to above their wounded value.
Those are the main three that I find most interesting. The bloodied and wounded rules where inspired by 4E, critical hits and fumbles are both of my own design. Enjoy.
