Prismatic Wasteland challenged rpg bloggers:
In January 2024, come up with a new resolution mechanic for a TTRPG and give it a name.
This needs a name so I thus name it “D6.5 Resolution”.
Pre-roll process
Whenever a character wants do so something, and the result is in doubt, the GM calls for a roll.
The character’s player states their character’s action and the intent of the action clearly.
The GM says whether they think success would be likely or unlikely. They might also use words like ‘very’ or ‘slightly’.
If the player doesn’t agree, then talk it out. Ensure that everyone’s understanding of the scenario is aligned.
The rest of this process can be hidden and done entirely by the GM, or open with player involvement. A hidden resolution relies on trust, whilst an open resolution invites collaboration.
D6.5 rolling process
The GM sets a target number from 1-5 and a d6 is rolled. Only if the result is over the target number then the action is successful.
| Target Number | Likelihood of success | Probability of success |
|---|---|---|
| 1 | Very Likely | 5/6 |
| 2 | Likely | 4/6 |
| 3 | Even | 3/6 |
| 4 | Unlikely | 2/6 |
| 5 | Very Unlikely | 1/6 |
If the GM wants to have degrees of success then they also roll a d3. The result can modify the success or failure to act as a critical result, or a limited result.
| D3 result | Success | Failure |
|---|---|---|
| 1 | Limited success/success with a problem | Critical failure |
| 2 | No effect | No effect |
| 3 | Critical success | Limited failure/failure with a benefit |
Analysis
I recently saw an rpg forum comment chain where folks were debating the merits and demerits of a particular game system. In particular, one poster was lamenting that a given system didn’t have degrees of success.
That particular debate struck me as rather silly. If you want degrees of success, I thought, just patch them on with a D3. Hence this mechanism.
I have used it to run Cosmos 2250 and Super Monster Friends. It works perfectly well for pseudo-star trek and pseudo-pokemon so it should work well for most anything.
It’s quick to use and returns you back to the conversation, and the GMs brain, which should together be your core game engine, with minimal issue.
The naming comes from the d6 and a possible additional d3, which is half of a d6. Hence D6.5
Coppers and Boars 
nice, love the classic “what, like its hard?” style of design. would you roll d3 for both? I feel like that’d be interesting sometimes, particularly because i love the crit success vs crit fail style – high stakes, high reward. Though the pairs you have already seem like another version of difficulty which i find interesting – as in, even though the check is very unlikely to succeed, you’ve mitigated against failure well enough that you get a crit success or at least a partial success. i think Errant called it position vs impact? anyway interesting to consider what factors/actions might affect one side or the other of a roll.
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If you need to roll over the TN, shouldn’t a TN of 1 be the most likely to succeed, not the least likely, and so on?
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If you’re supposed to roll over the TN, shouldn’t a TN of 1 be the most likely, 5 in 6 chance?
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Absolutely, thanks for catching that – I had flipped the order in half the table but not the other half
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