Most Dominions game mechanisms use something called the Dominions Random Number (DRN). When a random number is called for, the number used is actually a DRN. This is a roll of two six-sided dice (2d6) but with an additional bonus: if any individual die roll is “6,” one is subtracted, and then that die is re-rolled and added to the result. This is referred to as an “open-ended” 2d6 roll.
Example: The game calls for a DRN. Two dice are rolled and they come up 2,6. Because one of the dice was a “6,” one is subtracted from the total (making 7), and the die is rolled again. But this die is also a 6. So one is subtracted from the total (now up to 12) and a die is rolled again. It is a 4. The final result for this DRN is 16.
Note that if both original dice came up as 6, both would be re-rolled and added as above. If a die keeps coming up 6, it keeps getting re-rolled and added, which can very occasionally lead to large numbers. Dominions has a lot of situations where something is very unlikely to happen, like a militia soldier hitting an ethereal monster. However, in the real world of Dominions, very few things are actually impossible. To model this fact as closely as can be, the Dominions Random Number was created. With it, it is always possible for such an event to occur, which would not be the case if the roll was not openended. In some very few cases, there may only one six-sided die rolled. It is still open-ended, but in this case, the rules refer to it as a drn, in lower-case letters. An example is the dispelling of global enchantments.
Most die rolls in Dominions 5 involve one player rolling higher than another player using the DRN system. To give players some idea of how likely something is to happen, here is a table that shows the difference between two values on the left, and the chance of beating that value using two open-ended dice on the right.
What does this mean? It means that if you have a Jotun Moose Rider with attack skill 9 and your opponent has an Abysian Infantry with defense skill 10, your chance of beating him with two openended dice (and thus scoring a hit) is 38%. If the values were reversed, your chance of success would be 54%. Why the seeming disjunction? Because the “zero-point” is only 46%. Remember – the table shows the chance of beating your opponent. Thus, if you are evenly matched, you need to roll higher than he or she does on the same type of dice, and thus your chances of doing so are less than even. 46%, to be exact.
Sometimes the manual will state that a given effect requires a morale check (or some other ability check) “against” some number. This is simply a way of saying that a unit’s morale (or other ability) + DRN is compared to the stated number + DRN. So if a unit has to “take a morale check against 12,” this means the unit’s morale + a DRN is compared to 12 + DRN. If the unit has a morale of 10, the chart above would indicate that the chance of this unit passing the check is 30%.
A common situation you'll find yourself in is trying to win one at least one of a series of particularly difficult rolls, such as trying to get a Soul Slay cast through the Magic Resistance of a super combatant. Here are a few values to orientate yourself around what to expect:
|Difference||Single roll success||Expected rolls for success (1 in …)||Rolls needed for >80% chance of one success||Examples for magic pen against Magic Resistance of 18|
|-3||24%||4||6||Hard to resist magic pen roll|
|-7||8.20%||12||19||Standard magic pen roll|
|-11||2.60%||38||62||Easily negated magic pen roll|
|-15||0.76%||132||211||Easily negated + Antimagic source|