VARIANT: OPEN-ENDED ROLLS
By the time characters reach epic levels, the natural 1/natural 20 automatic failure/automatic success rule can often lead to frustrating results. The Dungeon Master’s Guide presents one option that can help alleviate this situation (a natural 1 is treated as a roll of –10 and a natural 20 becomes a roll of 30), but this just delays the problem. Eventually, even a –10 will hit anything and a 30 can’t land a hit.
The open-ended roll presents another option. Whenever you roll a natural 1 for a check—be it an attack roll, a saving throw, a skill check, or even an ability check—roll again and subtract 20 from the new result. Thus, if an epic-level fighter swung his sword at a frost giant and rolled a natural 1, he would instead roll a second time and subtract 20 from the second roll to determine his result. If you roll another natural 1 on the second roll, roll again and subtract 40, and so on, subtracting 20 each consecutive time a natural 1 is rolled.
On the other end, any time you roll a natural 20, roll again and add 20 to the new result. Thus, if the same frost giant were exposed to a meteor swarm from an epic-level wizard and rolled a natural 20 on his Reflex saving throw, he would roll again and add 20 to the new result. As with the natural 1, if a consecutive natural 20 is rolled on the second roll, you would roll a third time and add +40 to the result, and so on.
Note that an attack roll of a natural 20 still threatens a critical hit as normal, and the confirmation roll is made separately from any additional rolls made to determine the outcome of the initial attack.
Since this variant reduces the likelihood of creatures getting an automatic success or failure, it generally favors the PCs (as does any element that reduces random chance in the game).