GM Scenario Planning

Updated July 2026

Open Legend gives you a system flexible enough to run any kind of story — a dragon-haunted dungeon, a heist on a space station, a locked-room murder. This guide covers how to build a scenario worth playing, whatever genre you're working in.

What makes a good scenario

A scenario needs three things:

1. A clear situation — something is happening right now that requires the players to act
2. People with goals — NPCs who want things and will push back if thwarted
3. A change — by the end, something in the world is different because the players were there

You don't need a predetermined outcome. Plan the situation, not the solution.

Open Legend's genre secret

OL's 18 attributes were designed to describe any character in any story. The Extraordinary attributes — Alteration, Creation, Energy, Entropy, Influence, Movement, Prescience, Protection — are deliberately genre-neutral. The same attribute looks completely different depending on the fiction around it:

When planning NPCs and encounters, think about what an attribute *means* in your genre — not what it says on the label.

Fantasy

Fantasy scenarios live on stakes that are personal, mythic, or both. A village threatened by a curse feels different from an empire under siege, even if the dice rolls are identical.

What to prep:

• One location with history. Ruins, a cursed grove, a city that remembers better days. History creates texture without extra rules.
• An NPC with a secret. The mayor who knows what really happened, the merchant guild protecting its interests. Secrets give players something to find.
• The monster's reason. Even if players never learn it, knowing *why* the dragon hoards gold or why the bandits raid this road gives you better answers when they ask.

Challenge Ratings to use:

• CR 10 (Everyday) for wandering threats and minor obstacles
• CR 15 (Challenging) for boss-tier confrontations and contested social situations
• CR 20+ (Heroic) for legendary moments — reserve these; they should feel earned

Using Extraordinary attributes in fantasy: Let players describe the flavour of their magic. A character rolling Energy to attack isn't locked into fire — it could be lightning, cold, or radiant light. The dice don't change. The story does.

Science Fiction

Sci-fi scenarios work best when the technology creates the problem, not just the backdrop. A hyperspace gate that's been sabotaged, a colony ship with a resource crisis, a corporation covering up an accident — the tech is the dramatic engine.

What to prep:

• The information asymmetry. Who knows something the players don't, and why are they keeping it? In sci-fi, information is usually the real resource at stake.
• Two factions who both have a point. Rebels vs. the corporation, colonists vs. the AI administration. Players choosing between imperfect options creates more drama than heroes versus clear villains.
• One piece of gear that matters. A single environmental detail — the ship's failing reactor, the colony's last water processor — grounds abstract threats in something physical and ticking.

Reframing OL attributes for sci-fi:

• Learning and Logic handle hacking, engineering, and technical problem-solving — no special rules, just describe the action in genre terms
• Prescience works for scanner reads, tactical overlays, or predictive AI assistance
• Creation builds things: fortifications, improvised weapons, jury-rigged systems
• Movement covers teleporters, grav-boots, ship manoeuvring — anything that changes position dramatically

Pacing advice: Sci-fi scenarios often involve long-distance stakes (the station loses life support in six hours). Use that clock intentionally — give players a meaningful choice at the halfway point, not just a climax at the end.

Mystery

Mystery is the hardest genre to GM and the most rewarding when it works. The core rule: plan the crime, not the investigation. If you know what happened, who did it, and why, your players can find the truth from almost any direction.

What to prep:

• The truth. Write it out before you plan anything else. What actually happened? Where is the evidence? Who else saw it?
• Three clues minimum per piece of evidence. If they miss the bloodstain, maybe the witness mentions it. If they miss that too, maybe the suspect's alibi doesn't hold up. Mystery scenarios collapse when one missed clue locks everything.
• NPCs who lie for understandable reasons. Not because they're evil, but because they're scared, embarrassed, or protecting someone they love. Players feel cheated by arbitrary lies; they feel clever when they figure out *why* someone was lying.

Using OL attributes for investigation:

• Perception finds physical evidence — use it for noticing, not deducing
• Logic deduces meaning from what's found — what does the bloodstain pattern *mean*, not just is it there
• Deception and Persuasion play off each other in interrogation scenes — catching lies, applying pressure, building rapport
• Learning handles research: archives, databases, local expertise

The reveal: Don't plan how players solve it — plan what happens when the truth comes out. The accused's reaction, the consequences for the community, who else gets implicated. That's the real payoff, and it's entirely yours to prepare regardless of how players get there.

Structuring a session

Regardless of genre, most good sessions follow a loose three-part shape:

The hook — establish what's at stake and why players should care. Make it immediate. The village is burning *now*, not "the prophecy says it will burn."

The tangle — complications emerge. An ally has conflicting interests. The plan changes. Information was wrong. This is where player choices matter most — honour the consequences, even inconvenient ones.

The shift — something changes. The antagonist is stopped, escapes, or reveals something worse. The mystery resolves or deepens. Players leave the scene in a different position than they arrived.

You don't need a script for each part — just a sense of where the pressure is coming from and what happens if the players do nothing.

Using the Session Builder

Once you've planned the fiction, the Session Builder helps you weigh whether a fight is actually fair before your players are in it. It's available from the scenario create/edit screen — a new scenario takes you straight into it, and an existing one has a Session Builder row you can open any time.

Currently Open Legend only. Monster of the Week and Shadowdark aren't playable systems yet, so their versions of this tool aren't reachable.

Two modes

• Guided — a live Meter recalculates the moment you add or change a cast member. This is the mode to use while you're actually assembling a fight.
• Quick — no live Meter. You pick a difficulty band yourself, including a neutral Unrated state if you'd rather not commit to a number yet. Use this for scenes you're not weighing precisely, like a social encounter.

Building your cast

The top of the builder shows your campaign context — session number, seated players, and their levels, all pulled from your campaign roster automatically. You don't re-enter anything. A sit-out toggle on any seat lets you drop a player from this session's math (say, they're missing this week) without touching the campaign itself.

Add cast members from three sources:

• Custom — a one-off name, level, and role. Doesn't create anything in your NPC library.
• Roster — one tap to add any NPC already in this campaign's library.
• Browse Bestiary — search the Compendium's monster/NPC entries. Picking one asks for a level and whether to add it to your campaign roster — say yes and it copies a full NPC (attributes, HP, boons, banes) into your library for reuse; say no and it's used for this scene only, with nothing left behind.

Every cast member is a card with a tappable role chip — Standard, Minion, or Boss. Role changes how much that combatant weighs in the difficulty math: a Boss counts for four times a Standard's weight, a Minion for a third. Cycling a single combatant's role between Boss and Minion can swing a fight from Deadly to Easy — this is the single most powerful lever in the tool, worth understanding before you rely on the number it gives you.

Reading the Meter

In Guided mode, the Meter shows one of four bands as you build:

If you pick a band yourself that differs from what the Meter computed, the builder marks it Adjusted — both numbers save, and "Adjusted" also shows on the scenario's card back on Campaign Detail. Nothing stops you from overriding the Meter; it's a second opinion, not a rule.

Showing (or hiding) the rating from your players

A Reveal toggle controls whether your players see the difficulty band. It's off by default — "Hidden — only you see the rating." Turn it on if you want your table to see the stakes going in.

Before your session: the GM checklist

• [ ] What is the situation at the start of the scene?
• [ ] Who are the 2–3 most important NPCs and what do they each want?
• [ ] What does success look like? What does failure look like?
• [ ] What are the 3 most likely things players will try?
• [ ] What Challenge Ratings fit the difficulty you're aiming for? Run your cast through the Session Builder to check your instinct against the numbers.
• [ ] What loot is worth giving out this scene?
• [ ] Which participants need HP tracking — and what are their HP values?