So, I've got a d20 campaign world in the works, and in order to make combat reasonably fatal, and fairly realistic, and fit with the concepts of the game setting. So there's a lot of weird stuff here. Realize that all the classes will be custom built for the campaign world, so normal classes having hit dice and things like that won't screw this up.

Hit Points:
Your initial hit points are directly equal to your Constitution. These never increase, except in the case of certain feats, which grant increased hit points, or if your Constitution should increase.

Example: Han has a Constitution score of fourteen - as such, he has fourteen hit points. At level three, his player purchases the Survival feat, which grants a +2 to his hit points, making his total sixteen hit points. At level four, he gets a bonus to one of his abilities, and he chooses to apply it to Constitution. This brings his total to seventeen hit points.

The Smacking:
When you attack, in addition to adding your Base Attack Bonus to the attack, as well as your Dexterity modifier. Any points which exceed the target’s armor class add to the damage dealt, up to the maximum damage that could be dealt.

Example: Johnny the Spellsword currently has a +1 damage enchantment on his already powerful bastard sword (which has a 1d10 roll). This makes his maximum damage total 11 points. He’s first level, so his Base Attack Bonus is +1, and he has a Dexterity modifier of +2. His target, Flower the Imbued, has an AC of 14. He attacks, and rolls an twelve on his to-hit. When the +3 is added, his roll is effectively 15, which will grant an additional +1 to his damage. When he rolls his attack, he gets a three. He adds the +1 damage enchantment and the +1 from his attack roll, and gets five damage.

Dodge Dice:
At every level, including your first level, you are given an additional dice to your pool of Dodge dice (the size of the dice varies based on class). This pool refreshes every time you take a good rest period to full dice total. After you are attacked, you may choose to roll some of your Dodge dice. This will give you an AC bonus equal to the amount rolled for purposes of that attack. If this does not exceed the to-hit of the attack, you can roll additional dice until it does.

Example: Suppose, in the previous example, that Flower has only a few hit points left. Obviously, she doesn’t want to be sent down to the negatives, so she uses one of her dodge dice (a d8), and rolls a five. This negates Johnny’s attack, and gives her an opportunity to flee or cast a spell.

Will Points:
Will points are like normal D&D hit points, but they apply differently. They represent the character’s willpower to fight on, no matter how close he is to unconsciousness. They are typically lost due to either casting a spell or being particularly frightened during battle. Certain spells (or even some creatures) may inflict Will damage.

Your Dungeon Master may give you bonus Will points in certain situations, and the special abilities of some characters give their allies bonus Will points. No healing spell cures Will damage - only rest.

Example: Flower chooses to use her spell-like ability Fright to deal 1d10 + Cha modifier Will damage. Since her Charisma modifier is +2, any target will take between 3 and 12 Will damage. This could easily knock a low-level target cold. Since in the Imbued class description it clearly specifies that the spell level (in this case 2) is taken in Will damage, she takes two Will damage.