Open-Ended Dice Rolls

In the d20 system, all resolution rolls are attempted by rolling a single 20-sided die. In the core rules, in combat or when saving against spell-like effects, a natural 20 is always a success, and a natural 1 is always a failure. The same is not necessarily true for Skills.

I intend to change this to an open-ended system which will be used for all resolution rolls.

Rolling High

If the initial resolution roll is a natural 20 (or within the weapon's Threat Range for an attack), roll again and add the result to the initial score. If that roll is also a natural 20, roll again and add the result again, and so on. Then add or subtract any appropriate modifiers for a final result.

If the result is 20 or more greater than that required for success, then you have achieved a Critical Success.

Example:
Throg the Muscular (STR 16) smacks Woolly Will the Wild Wizard (AC 18) with his +2 Axe of Wizard-Whacking. Throg rolls a natural 20, and so he rolls again, for an additional 12. Throg adds all his modifiers, a total of +9 (+3 for Strength, +4 Base Attack Bonus, and +2 for his magical axe) for a final result of 41. He got a score 20 or more higher than poor Will's AC of 18, so Will takes a Critical Hit and has his arm cut clean off.

Throg is then attacked by Will's enraged familiar, a repulsive hopping toad-demon with an AC of 16. Throg smites it mightily, and gets another natural 20! Throg is hot tonight! He rolls again, but this time only manages to add 4 to his 20. Even with all his modifiers, he can only manage a final score of 33, so although the blow connects it is not a Critical Hit.

Examples of Critical Successes

Attack: The blow is a Critical Hit, and damage is resolved using the Critical Hits chart.
Save: If the spell allows a save for ½ damage, instead no damage is taken at all. Other spell effects are minimised — minimum damage, minimum duration, etc.
Skill: Perfect execution of the skill. A Healing roll would return a hit-point or two, a Climb roll would allow a full move instead of half, etc.

Rolling Low

Similarly, if the intial resolution roll is a natural 1, the die is rolled again and the result is read as a negative value. For example, a second roll of 12 would be read as a resolution roll of negative 12. If the second roll is also a natural 1, then roll again and add 20 (reading the result as a negative value), and so on. Add or subtract any appropriate modifiers for the final score.

If the final result is 20 or more less than that required for success, then the result is a Fumble of some kind.

Example:
Bob the Burglar (DEX 18, 6 Ranks in Lock-picking) is trying to pick a lock with a DC of 15. He rolls a 1, and rolls again for negative 16. He adds his modifiers for a final total of -16 + 4 + 6 = -6, which is 21 lower than the DC of 15. He has Fumbled, and his lockpick breaks off inside the lock, jamming it irretrievably.

His team-mate Throg, losing patience, decides to bash the door down by brute strength and charges at it head first. This is fairly sturdy door, so the DM decrees that the DC to break it down is 15. Throg smashes into the door and also rolls a 1, rolling again for a total of -6. He adds his STR modifier (+3) for a final total of -3. he has failed to burst open the door, but because his final total wasn't 20 less than the DC of 15, he hasn't fumbled and can try again.

Examples of Fumble Results

Attack: If in melee combat, the attacker draws an immediate Attack of Opportunity. If making a ranged attack, the character may lose or break their weapon. If the fumble is bad enough, they may even hurt themselves or their team-mates.
Save: Suffer the maximum possible effect of the spell — maximum damage, maximum duration, etc.
Skill: Catastrophic failure. Equipment breaks, traps are triggered with no save, attempted healing rolls actually make the patient worse. If the Skill roll normally allows a retry on failure, the fumble alters circumstances so that no retry is possible (the exact circumstances are at the discretion of the DM).

Criticals and Fumbles

It is important to note that the possibility of a critical or fumble occurs only if the intitial resolution roll is rolled naturally, i.e. before modifiers, 20 (or within the Threat Range) or 1.

Even though Telecomxtra, Demon Lord of Sloth and Greed, may have an AC of 47, that doesn't mean that every time someone makes an attack roll of less than 27 they have fumbled their attack. If they didn't throw a natural 1, then they merely miss and do the demon Lord no damage with that attack.

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