@pemerton out of interest when you use something like this in play, do you discuss upfront what the runes are should the PC fail their roll? Does the PC know that should they fail the roll, the runes will definitely be something negative? or perhaps even accidentally triggered?
In MHRP, by default the Doom Pool is simply an opposition dice pool. So the most immediate consequence of failing an action is wasting your turn. But the GM can spend Doom Pool dice to trigger effects on a successful roll of the opposition pool. It's also possible to give a Scene Distinction a SFX (eg On a successful reaction, you may use your effect die as if you had succeeded on an action) but the Strange Runes didn't have an SFX like that, which would probably fit better with Magic Runes.
So the player knows that, if they fail, there is the risk of a Doom Pool spend (and the worse they fail, the bigger the effect die of the reaction which will be converted into an actual effect). The effect itself, like everything in MHRP, would be die-rated (analogously to the d12 Lost in the Dungeon complication) and would figure in fictionally appropriate opposition pools.
As to
what that effect might be, generally I rely on the trajectory of play to establish an implicit sense of exactly what is at stake. Sometimes I will be overt, eg if I think I have a brilliant idea for a consequence, or I want to taunt the player, or perhaps if the player asks.
Other RPG systems that I play regularly take different sorts of approach. For instance, in Burning Wheel on a failure generally the GM should be narrating a consequence that sets back the PC from the perspective of their intention. There is no "pool" or "cost" that the GM needs to draw on. Here's an example that pertains to identifying a strange object (
it's from me posting on rpg.net):
One of the players had bought rulebooks and built a BW PC (a noble-born Rogue Wizard inspired by Alatar, one of Tolkien's blue wizards of the East). I had built a PC for another player to show him what the system was capable of - a spell-using necromancer ranger/assassin (hunter-wizard's apprentice-rogue wizard-bandit). . .
The rogue wizard, Jobe, had a relationship with his brother and rival. The ranger-assassin, Halika, had a relationship, also hostile with her mentor, and the player decided that was because it turned out she was being prepared by him to be sacrificed to a demon. It seemed to make sense that the two rival, evil mages should be one and the same, and each player wrote a belief around defeating him: in Jobe's case, preventing his transformation into a Balrog; in Halika's case, to gain revenge. . . . each also wrote up a immediate goal-oriented belief: I had pulled out my old Greyhawk material and told them they were starting in the town of Hardby, half-way between the forest (where the assassin had fled from) and the desert hills (where Jobe had been travelling), and so each came up with a belief around that: I'm not leaving Hardby without gaining some magical item to use against my brother and, for the assassin with starting Resources 0, I'm not leaving Hardby penniless. . . .
I started things in the Hardby market: Jobe was looking at the wares of a peddler of trinkets and souvenirs, to see if there was anything there that might be magical or useful for enchanting for the anticipated confrontation with his brother. Given that the brother is possessed by a demon, he was looking for something angelic. The peddler pointed out an angel feather that he had for sale, brought to him from the Bright Desert. Jobe (who has, as another instinct, to always use Second Sight), used Aura Reading to study the feather for magical traits. The roll was a failure, and so he noticed that it was Resistant to Fire (potentially useful in confronting a Balrog) but also cursed. (Ancient History was involved somehow here too, maybe as a FoRK into Aura Reading (? I can't really remember), establishing something about an ancient battle between angels and demons in the desert.)
My memory of the precise sequence of events is hazy, but in the context the peddler was able to insist on proceeding with the sale, demanding 3 drachmas (Ob 1 resource check). As Jobe started haggling a strange woman (Halika) approached him and offered to help him if he would buy her lunch. Between the two of them, the haggling roll was still a failure, and also the subsequent Resources check: so Jobe got his feather but spent his last 3 drachmas, and was taxed down to Resources 0. They did get some more information about the feather from the peddler, however - he bought it from a wild-eyed man with dishevelled beard and hair, who said that it had come from one of the tombs in the Bright Desert. Jobe, being unable to buy Halika any lunch, suggested he might be able to find some work for them instead.
The consequence of failure - ie that the feather is cursed - wasn't expressly flagged in advance, but given the characters, their backgrounds and situation in the fiction, and their Beliefs, it flowed pretty naturally. My general test for this is whether the player groans or thinks its unfair. That didn't happen here!
At least for the rest of this session, the curse didn't have any mechanical effect. Rather, it provided context for narrating further failures, eg like this one:
Jobe, having both nobility and sorcerers in his circles, and a +1D affiliation with both (from Mark of Privilege and a starting affiliation with a sorcerous cabal), initially thought of trying to make contact with the Gynarch of Hardby, the sorceress ruler of that city. But then he thought he might start a little lower in the pecking order, and so decided to make contact with the red-robed firemage Jabal (of the Cabal). With Circles 2 he attempted the Ob 2 check, and failed.
So, as the 3 PCs were sitting in the Green Dragon Inn (the inn of choice for sorcerers, out-of- towners and the like), putting out feelers to Jabal, a thug wearing a rigid leather breastplate and openly carrying a scimitar turned up with a message from Jabal: Leave town, now. You're marked. Halika noticed him looking at the feather sticking out from Jobe's pouch as he said that: it seemed that the curse had already struck!
And it also contributed to framing of scenes, like here:
The trip to Jabal's tower took them through the narrow, winding streets of the city. When they got there, Jabal was suitably angry at his Igor-like servitor for letting them in, and at Athog for not running them out of town. They argued, although I don't think any social skill checks were actually made. Jabal explained that the curse on the feather was real, from a mummy in a desert tomb, and that he didn't want anything to do with Jobe while he was cursed. Jobe accepted his dressing down with suitable Base Humility, earning a fate point. (The second for the session from a character trait. . . .)
Sorry if the answer is a bit overlong, but I wanted to take the opportunity to provide some examples of the differences between systems that in this thread are often getting lumped together in remarks about how "narrativist" or "narrative" RPGs work.