Rolling the Dice (or Not)

Know When Not to Roll
Contests in Isekai are frequently resolved by rolling dice. In many situations, however, the GM should avoid rolling dice.


 * Don't Roll Unless Failure is Interesting
 * Don't Roll Dice if You Can Role-Play

If failure is not an opportunity for interesting play, rule the action successful without a roll, or make a roll only for the cost of success. If an action can be resolved by interaction with an NPC, role-play the interaction to determine its result. If a die roll is needed, assign numbers of dice to the PC based on his roleplaying, and to the NPC based on your knowledge of his character.

Die-Rolling Mechanics
Each side rolls a pool of ten-sided dice. The pool with the highest single die wins. Compare the rolls to determine the winner's number of Victories, which equal the greater of:


 * 1) The winner’s highest die minus the loser’s highest die, or
 * 2) The number of the winner’s dice which are higher than the loser’s highest die (to a maximum of 9).

In case of a tie, remove both tied dice and consider the remaining dice; repeat as necessary. If ignoring ties leaves the loser with no dice, the winner gets only 1 Victory.

Variations on the Die Roll
The basic mechanic is adaptable to all situations, which allows players to try anything that they can imagine, whether or not the game has a mechanic for that action. However, for routine situations the basic mechanic can require more time than is fun. The additional mechanics below make play faster.

3 Types of Die Rolls
Action Rolls are for making an attack or taking any other action. Defense Rolls are for resisting an attack or other action. Second Rolls add dice to a die pool. A Second Roll cannot change who wins, but it can change the number of Victories. Ignore any Second Roll which reduces the rolling character’s number of Victories. Second Rolls should be used sparingly, as they slow the game.

See also Combat Rounds

Quick Rolls
Normally Bob's Action Roll is compared against his foe's Defense Roll. Quick Rolls dispense with Defense Rolls. Instead they directly compare Action Rolls to determine winners and victories. These are mostly used for contests between NPCs.

Advantage and Disadvantage
Dis/Advantage allows modification of an already-rolled result, and modification of some but not all uses of a roll. It is also a handy modifier for ad-hoc rulings.

With Advantage Bob counts his highest die twice; with Disadvantage he ignores his highest die. Advantage and Disadvantage do not stack, but some situations may impose Double Disadvantage (ignore highest 2 dice).


 * Initiative Advantage doubles the high die only for the purpose of determining who goes first.
 * Hit Advantage doubles the high die only for the purpose of determining who wins the contest.
 * Damage Advantage doubles the high die only for the purpose of determining how many Victories the winner achieves. Damage Disadvantage can never reduce a successful hit to less than 1 Victory.

Thresholds
Thresholds are pre-rolled values which can substitute for a normal die roll. In some cases Bob's Action Roll must exceed a certain Threshold for his action to succeed. If the Threshold is not met the action fails and there is no need for a Defense Roll. In some other cases the Threshold is the only defense which Bob must overcome. Numbers of dice not on this chart should be rounded to the nearest value which is on the chart. In the rare case where the number of victories matters and the die roll ties with all the values listed below, consider the next value to be a 1.

Thresholds can be used instead of die rolls to save time, and can represent additional barriers to success such as local magic resistance. They are also useful for obstacles of fixed difficulty, such as climbing a wall, and for "passive" perception, ie. being noticed by someone who is not actively looking.

Take-Away Dice
Some actions can act on several targets, or in several areas, or over several rounds. A roll is made normally for the first target, round, or area. Subsequent targets/rounds/areas use the same roll with the highest die removed after each target or round. Effect ends when highest remaining die < 9.

Area Effects: Take-Away dice allow area effects to diminish away from the center of the effect. This allows area effects to be large without being either over-powered in total or under-powered at the center of the effect. Take-away area effects normally use a circular 15’ diameter center "ring" surrounded by 5’ wide donut-shaped rings. Each Bob takes damage at end of turn based on highest damage area which she occupied or moved through.

Multiple Targets: Take-Away damage can be inflicted on several targets, at full effect for the 1st and -1 die for each subsequent target. For some uses multiple target will end on the first successful save, instead of when highest remaining die < 9.

Slow Rolls
Slow Rolls are used to generate a random duration for some effect. When a random duration needs to be rolled, each roll should be delayed until needed. For example, if some effect is to last for 3d6 rounds then you roll 1d6. Roll the second die when the round count reaches the first dies result. Roll the third die when the round count reaches the sum of the first 2 dice. This simulates the character's uncertainty about the length of the effect.

Magic Numbers
Use Magic Numbers to simulate unpredictability. The Magic Number is a second random value derived from the same die roll by grouping the dice by the face (eg. 8) that they are showing and determining whether the count of dice in each group is even or odd. Note that any group with no dice is considered even. (This produces higher numbers and less-random results when rolling very small numbers of dice.)

Simple Magic Numbers count only the groups with an even number of dice. If the 10s group is even, the Magic Number is the count of consecutive even groups beginning with 10. These values are mostly used for relatively uncommon effects such as weapon breakage, magic misfires, etc.

Complex Magic Numbers: More complex results can be obtained by also using the count of odd groups. Instead of zero, groups with an odd number of 10s are treated as the negative of the count of consecutive odd groups. This produces two values, one positive and one negative, for each of the frequencies in the chart above. For example, the Magic Number can always generate a d4 value, and if there are enough groups you can generate a d8 value by looking at the two groups of dice which come after the Magic Number: if they match add 4 to the d4 result, otherwise use the d4 result as is.