Chapter 5 — Running Merretia

Most of what happens at your table runs on rules your players already know. This chapter is the other part — the handful of systems that are Merretia’s own, and how to make each one land rather than merely resolve. If you read one chapter of this book before your first session, read this one.

Running magic as debt

The cost engine (PHB Chapter 6) is the heart of the game, and it only works if you, the GM, treat the two clocks as real.

• Let the clocks fill. Don’t fudge a caster’s Strain or Fray down to be nice. The tension of the whole system is watching the number climb toward the cap. A caster who never approaches their cap is a caster whose power costs nothing — which is the one thing this world forbids.
• Pace rests deliberately. Because Strain clears on a short rest and Fray does not, you control a caster’s arc mainly by controlling rests. Give the party a short rest and the Order-casters reset; withhold long rests of genuine stillness and the Chaos-casters carry their Fray — and their dread — into the next fight. A dungeon that denies stillness is a Chaos-caster’s nightmare, and you should use that on purpose.
• Never touch the Loss Menu unbidden. When a Chaos-caster crosses the 75% Fray threshold, they roll against the six losses they wrote. You do not invent losses, and you do not roll for them. Your job is to honor the loss the dice pick — to play out, with weight, the character forgetting their sister’s laugh or losing their certainty. Make it a scene, not a line item. This is the most emotionally powerful moment the system produces; treat it that way.
• Overchannel is a player’s choice; the Break is yours to make terrible. When a player chooses to Overchannel, let them — it’s the bargain the system offers. The Break (pushing past the cap) should be rare and genuinely frightening: an Order-caster dropping at 0 HP, a Chaos-caster’s Unraveling. Don’t threaten it lightly, and when it comes, don’t soften it.

Awarding Conviction

Conviction is the one advancement lever that isn’t automatic — it rises only when you judge the story has earned it, and it’s how you tell your players, mechanically, what this game is about. Guidance:

• Award it for belief held at cost, never for winning. A character raises their Conviction when they keep an oath that hurt to keep, moved a crowd when it was dangerous, refused the Hollow when it would have been easy, or acted dead-center of their Tenet when it cost them something real. The trigger is paid conviction, not success.
• Cadence: roughly once per tier of play per character (so a Conviction of 3–4 by mid-campaign, 5 rarely and late). If everyone’s Conviction is climbing every session, you’re rewarding action, not belief — tighten it. If it never moves, you’re not watching for the moments — loosen it.
• Name it when you give it. “That cost you, and you did it anyway — your Conviction rises to 3.” Said aloud, the award teaches the table the game’s values better than any rules text.

The visible caster in play

The eye-flash (PHB Chapter 11) is a gift to you as a GM — use it for tension:

• Telegraph enemy casters. When an enemy’s eyes go cyan, your players know lightning is a beat away and can act. This turns enemy casting into a readable threat and rewards attention, not just initiative.
• Make hiding a caster’s tell matter. A player who wants to cast unseen has to solve a problem (cover, darkness, an eye-shroud, distance) — reward the setup with genuine surprise. An assassin-caster who arranges to never be seen casting is doing exactly what the world fears.
• Voided-black eyes are a set piece. The first time the party sees someone’s eyes go black instead of a colour, let it land in silence. That’s a Hollow-user, and everyone at the table who’s read the world knows what it means. Don’t over-explain it.

Oaths at the table

This is a civilization of sworn word, and several Callings and peoples put oaths on the sheet (the Vowbound’s Vows, the Halkari’s Stand, the Sulevri’s Am-thread). Run them as live wires:

• Honor the benefits generously and the breaks seriously. While a vow holds, give the bonus freely. When one breaks, the mechanical penalty is real — and a clever enemy will engineer the break. Forcing a Vowbound to choose between two of their vows, or maneuvering a Halkari into a position where holding the Stand means letting the innocent die, is exactly the kind of pressure this world is built to apply.
• Let oaths generate plot. An oath a character can’t take back is a story hook you didn’t have to write. Ask, early, what each oathbound character swore — and then bring them the day it costs them.

Keeping non-casters in the miracle business

Because magic is rare, most parties will have magic-free members, and the world promises they’re never lesser. Two things keep that promise at your table:

• Let unshaped Faith matter. Any character can lend Faith (PHB Chapter 6/10). Frame the moments where the Kardun’s hand on a dying friend’s chest is the thing that saves them — the martial characters have a miracle too, and it costs them something.
• Give martial problems, not just magical ones. A locked door, a debt to negotiate, a wall to breach, a duel of honor — build scenes where an oath-knight or an unbreakable wall is the answer, not a spectator to the caster’s spotlight.

Tone, warfare, and the shape of a campaign

• The exhausted elite. When you run soldiers, run the doctrine (see ): armies are common troops with arc-locks and oath-metal, and a few terrifying, guarded channelers. Commanders “count flashes like cannon.” A single Working can turn a battle — and then that caster is spent. Let the players feel both halves of that.
• The debt-economy. In Sulamir a signature is nearly money and everyone owes someone by nightfall. Make debts, favors, and guild allegiances the connective tissue of your intrigue. “Who does this cost, and who do they owe?” is the most useful question you can ask about any Sulamir scene.
• The Dome and the Seepwar. Sulamir cannot be conventionally besieged — the Dome holds against armies and only a kaiju-scale assault over hours could crack it. So city war isn’t sieges; it’s the Seepwar, the quiet fight against Hollow incursion the shield can’t stop (Chapter 8). Frontier war is the opposite — no Dome, real sieges, powder and steel. Know which war your campaign is fighting.

Difficulty, in this system

A note for encounter-building: a channeler is artillery, not infantry — glass, expensive, and decisive for a few rounds. Build enemy forces the same way (a Thread of casters behind a Cage of elites), and remember that grid pressure and denied rest are difficulty levers as real as monster numbers. The scariest thing you can do to a well-supplied party is take them somewhere the recharge posts end and the stillness never comes.