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A friend of mine is interested in adding an explosive mechanic to the One Roll Engine for his home-brew system. This mechanic is to provide for virtually impossible feats and remarkable failures. However, he doesn't want the statistics of the game changed overmuch.

How can I add "exploding dice" to the ORE in such a way to allow for absurdly-impossible lucky shots to happen (equivalent of rolling four 1's in a row in Ars Magica) and absurdly-bad critical failures, but at very low frequencies?

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So your friend wants to add additional rolls to the One Roll Engine? – Jadasc Mar 30 '11 at 9:46
Amusingly, yes. – Brian Ballsun-Stanton Mar 30 '11 at 9:59
up vote 2 down vote accepted

There is no obvious mechanic but one that make sense to me is:

If there are more width dice than the character needs to succeed then they can be transferred to increase the height, say, at a two to one ratio.

So if for example you got 10x10 and you only need a width of 4 then you can change this to a 4x13. Results above 10 are virtually impossible feats.

It might be best if they players does not know what the required widths are, then you can get results like, "you tried too hard to get that /arrow in an arrow shaft shot/ and the bow snapped".

Also for remarkable failures as the number of dice increase it become unlikely for any fail, so may be you should use the width again. If the width of the roll is two (say) less than the required width, then it is a fumble and the height, or rather the lack of it, gives you the level of fumble. Hence say a player get 6x3 and decides to shift this to 2x5 thinking that is is a better result, but unknown to them a width of 4 was required, then, this is a level 3 fumble.

Hope that helps.

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Often the necessary width will be obvious, just because of the way the system works. Incidentally, there is some discussion of this kind of mechanic (called "squishing") in the Reign Enchridion. It's introduced on p 17, and its implications are discussed on pages 67, 73, and 75 in specific Disciplines that enable it. The short is that whether it's useful or not and how much depends heavily on the skill being rolled, even when the player knows the numbers they need; and it will often break games when allowed on martial skills. This is an interesting suggestion, but proceed with caution! – SevenSidedDie Apr 1 '11 at 16:19
Thanks, never played the game. I remember went the game system first came out and I thought, interesting idea but unlikely to play that system. – David Allan Finch Apr 4 '11 at 10:20
It's nicely-adaptable to various genres with surprisingly little work since it's not so finely-grained as other universal systems like GURPS. That makes it a good drop-in replacement system for a setting you like with a system you hate, or for unusual homebrew settings. It fills a similar niche to Savage Worlds in that way. – SevenSidedDie Apr 4 '11 at 18:00

(Community wikied, because I don't like earning points on self-answers)

Reading the responses, here's one suggestion, please improve:

Unpaired ones are Bad. Unpaired tens are Good. If a player rolls an unpaired 1, she must keep the 1 and reroll the die. If it results in a pair, the pair acts as gobble dice against her own rolls. Subsequent 1's must be rerolled as well.

If a player rolls an unpaired 10 (hard dice and wiggle dice don't count), she may choose to keep the 10 and reroll the die, rerolling 10's until a 10 is not rolled.

Thus, the 1's tend to (rarely) eat successes, increasing the odds of a crit-fail. 10's increase the chance of successes, but only if they're not already in a pair.

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As you choose, but I think it's a good solution. – Jadasc Apr 2 '11 at 15:01

After looking at John H. Kim's chart of ORE's probabilities, one could conclude that high widths are a good way to represent the "absurdly impossible lucky shot." However, this doesn't allow for critical failure, or the chance for someone of low skill to do something extreme.

One way of getting the swingy effect desired could be to give extra benefits if all your dice are in a single set (that is, they all match), and a corresponding penalty if all your dice are unmatched but in sequence — what you'd call a "straight" in poker. Neither of these take into account the effects of hard, fixed, or wiggle dice.

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Nor does it provide for "exploding dice" But it does present an interesting direction of research. – Brian Ballsun-Stanton Mar 30 '11 at 10:00
The usual definition of "exploding dice" is "reroll and add/subtract." In ORE, you neither add nor subtract — you simply look for matches. But that does suggest an idea. Editing. – Jadasc Mar 30 '11 at 10:03
@Brian Ballsun-Stanton - I would remind you that both the "straight" and "flush" are more likely to occur in small pools - so if it's intended solely to allow low-skill characters to occasionally achieve unlikely successes, then sure. But if you use that mechanic, you put critical successes further and further out of reach as characters get better - probably not the effect you intend. – gomad Mar 30 '11 at 17:15
@gomad - Actually, that might be a feature, rather than a bug. Skilled characters are reliable, time and time again. Novices mostly fail, occasionally get into deep trouble, and occasionally get beginner's luck — so you can't discount them entirely. If you're looking for the kind of moments that an "exploding" system offers, that's not bad. – Jadasc Mar 30 '11 at 17:37

I suppose one way you could emulate this is by re-rolling loose dice. If you get another set or add to an existing one, keep rolling. If you get loose dice again it cancels out one set. If you have no sets it's a critical fail.

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Whenever you roll a 10 (i.e. a zero on a d10), reroll it and roll an extra die, which adds into the pool.

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