# 2d20 System Explained: Which Modiphius TTRPG Should You Start With? Published: 2026-11-05 Updated: 2026-11-05 Compare Star Trek, Dune, and Fallout 2d20 games to pick the right Modiphius RPG based on play style and learning curve. ## Article I’d start with [Star Trek Adventures Second Edition](https://modiphius.net/en-us/products/star-trek-adventures-the-roleplaying-game-second-edition-core-rulebook) for [team-based](/category/team-based) missions, Dune for political intrigue, or Fallout for gear-driven survival. All three use the same basic roll: roll 2d20, count successes, and compare them with the task’s Difficulty. But their rules create different experiences at the table. My advice: pick the play style first, then the book. A starter set offers a guided first game; a core rulebook supports character creation and longer campaigns. Quick Comparison Game Best for Rules and learning curve Where I’d start [Star Trek Adventures](/item/startrekadventures) Second Edition Teamwork, science, diplomacy, and space missions Moderate; crew and starship rules take practice Second Edition Starter Set [Dune: Adventures in the Imperium](/item/duneadventuresintheimperium) House politics, espionage, and negotiation Moderate to high; tracking assets and rival interests matters Agents of Dune starter set or Core Rulebook [Fallout: The Roleplaying Game](/item/fallout) Scavenging, firefights, and scarce supplies Moderate to high; gear and combat add bookkeeping Fallout Starter Set I’ll compare genre, rules, resources, and starting products so you can choose what fits your group. Learn basic tests first, then add ship actions, House schemes, or survival rules as you play. Check print and PDF options - and current stock - before buying. Which [Modiphius](https://modiphius.net/en-us) 2d20 RPG Should You Start With? [Modiphius](https://modiphius.net/en-us) [2d20 System](https://modiphius.net/en-us/blogs/news/2d20-basics?srsltid=AYCX9vKdpW_cZSooi-e4Qvo19Zv59S44LVBo3oV1avimsNSnCCjrfKx4) Made Simple ## How 2d20 Works: Shared Rules and Game Differences The core roll stays the same, but each game puts it to work differently. The target number tells you what each die must roll; Difficulty tells you how many successes you need. Add the two relevant ratings, roll 2d20, and count one success for each die at or below the target number. Meet the Difficulty to succeed. The rating names vary by game. Example: A rating of 7 plus a rating of 5 gives a target number of 12. Roll 7 and 11, and both dice succeed: two successes. Against Difficulty 1, one success completes the task; the other is excess and normally generates one Momentum, or one Action Point in Fallout. Criticals usually count as two successes, but each game sets its own trigger range. In Fallout: The Roleplaying Game, a natural 1 counts as two successes. With a Tag Skill, results at or below that skill’s rating count as criticals, too. Don’t assume that threshold applies to another 2d20 game. Spendable resources also work differently across games. They can buy extra dice, provide information, or improve an outcome, depending on the rules. Some options give players an immediate advantage while adding to the GM’s resources. Check your game’s costs, timing, and allowed spends rather than carrying rules over from another title. These choices shape how players weigh opportunity against danger - and how each game puts those successes under pressure. Mechanic Shared foundation What varies by game Task resolution Combine two ratings, roll 2d20, and count successes against Difficulty. Rating names, assistance, modifiers, and special tests differ. Critical successes A qualifying die usually earns two successes. Skills, focuses, Tag Skills, and edition-specific rules determine the threshold. Player resources Excess successes generate a spendable resource. Star Trek and Dune use Momentum; Fallout uses AP. Each has its own spending options and limits. GM resources A GM-controlled pool can strengthen opposition or increase danger. Star Trek and Dune use Threat; Fallout uses GM Action Points. Rules for gaining and spending these resources differ. Character resources Individual abilities change what characters can do. The names and effects of character-specific mechanics vary by game. Combat or conflict Conflicts build on the basic test. Star Trek adds personal, social, and starship procedures; Dune emphasizes influence and intrigue; Fallout adds tactical actions, equipment, and hazards. For a first session, teach target number → roll → count successes → compare with Difficulty. Then introduce your chosen game’s resource rules. Players can learn the shared roll once, but each game’s resources and conflict rules need separate attention. The next sections look at how Star Trek Adventures, Dune, and Fallout use that shared engine to create different tones, pacing, and levels of complexity. ## 1. Star Trek Adventures Second Edition ### Genre and play style Choose this for optimistic [science fiction](/category/science-fiction) and collaborative problem-solving. Modiphius’s Star Trek Adventures Second Edition puts you in a starship crew on episodic missions: investigating anomalies, meeting unfamiliar cultures, solving scientific problems, and occasionally fighting. Each crew specialty gives players a different way to contribute. It’s a balanced introduction to 2d20 rather than a combat-first game. ### Rules complexity Compared with the shared 2d20 basics, Star Trek leans hardest on teamwork. Of the three games, it’s the most approachable for groups that prefer cooperation over optimization. Accessible doesn’t mean rules-light. The core rulebook covers characters, crew, and starship procedures. Tasks pair an Attribute with a Discipline, while Assists let other characters pitch in when their actions help. Start with ordinary tasks and teamwork, then add starship encounters. ### Resource and conflict systems Momentum gives the crew advantages, while Threat lets the GM apply pressure. Values shape play, and Determination powers key efforts tied to them. Personal combat involves positioning and the consequences of injuries. Social conflict focuses on persuasion and competing goals. Starship procedures have the steepest learning curve. Players must work together across bridge roles, ship systems, repairs, and defenses. ### Starting products For an open-ended campaign, get the [Star Trek Adventures Second Edition Core Rulebook](https://modiphius.net/en-us/products/star-trek-adventures-the-roleplaying-game-second-edition-core-rulebook?srsltid=AYCX9vL6ueARLDaq8k8JT-urM7LdQFxBysa26s62WWSpQUzXfm9Qn_XG). It’s available in print or PDF and contains the full rules. For a guided introduction, choose the [Star Trek Adventures Second Edition Starter Set](https://modiphius.net/en-us/products/star-trek-adventures-the-roleplaying-game-second-edition-starter-set?srsltid=AYCX9vK-FdGjdxf_OkQLi7cEC8pGQE3mTil5Yl2QUzQoNHnARHHb5r3b). It includes a rules booklet, the three-part Infinite Combinations campaign, seven pregenerated player characters, a ship sheet, five d20s, reference sheets, and Momentum, Threat, and Determination tokens. Move on to the Second Edition Core Rulebook afterward. If your table prefers politics and leverage to exploration, Dune: Adventures in the Imperium is the sharper fit. ## 2. Dune: Adventures in the Imperium ### Genre and play style If Star Trek is about collaboration, Dune is about leverage. Choose Dune for political intrigue, espionage, and choices with lasting consequences. Characters serve a noble House and advance its interests through secrets, alliances, economic pressure, and violence. Every concession can create a debt or another obligation. Dune sits between Star Trek’s cooperation and Fallout’s focus on combat. It suits players who prefer negotiation and competing loyalties to frequent tactical battles. ### Rules complexity The main challenge is keeping track of information, assets, and faction pressure. Start with the situation in the story: state your goal and approach before rolling. Assets provide tools, contacts, and leverage, while Architect play lets you direct agents and House assets. Begin with one House, a small cast of rivals, and a clear objective. Between sessions, track promises, debts, and faction reactions. Play becomes less about tackling problems head-on and more about setting the terms of the next move. ### Resource and conflict systems Momentum and Threat fuel leverage, complications, and shifting alliances. ### Starting products Start with the Dune: Adventures in the Imperium Core Rulebook. It includes the adapted 2d20 rules, a setting overview, character and House creation, GM guidance, and an introductory adventure. Supplements are optional. If your group wants more direct action and scavenging, Fallout is the better fit. ## 3. Fallout: The Roleplaying Game ### Genre and play style Fallout is the clearest choice for players who want a combat- and gear-driven 2d20 game. Set in post-nuclear America, it focuses on wasteland travel, hazardous sites, scavenging, and faction play. There’s room for negotiation, stealth, problem-solving, and rebuilding alongside tactical firefights. You can play vault dwellers, ordinary wasteland survivors, ghouls, super mutants, and robots such as Mister Handy. ### Rules complexity Complexity is moderate to high. Core tests are easy to learn, but Fallout layers on SPECIAL attributes and Perks, ammunition, armor, weapon qualities, and hit locations. Scarce supplies and radiation make managing equipment a regular part of play. Compared with Star Trek’s teamwork and Dune’s intrigue, Fallout puts the most weight on gear. ### Resource and conflict systems Combat and the search for supplies put AP and Luck at the center of play. Extra successes become shared Action Points (AP), capped at 6. Players spend them on bonus dice, more actions, information, or extra damage. The GM has a separate AP pool for complications and enemy advantages. Luck is a limited character resource. You can spend it to substitute the Luck attribute, change initiative timing, or reroll a d20 or up to three Combat Dice. Combat Dice determine damage and weapon effects, while armor, hit location, range, and cover give players more decisions during firefights. ### Starting products Modiphius’s [Fallout: The Roleplaying Game Starter Set](https://modiphius.us/products/fallout-the-roleplaying-game-starter-set) includes a rulebook, the Once Upon a Time in the Wasteland quest book, pregenerated characters, and custom dice. It’s the pick for a guided entry. The Core Rulebook supports full campaign play with full character creation, more equipment, and tools for encounters, locations, and loot. Groups focused on settlements can add [The Settler’s Guide](https://modiphius.net/en-us/products/fallout-the-roleplaying-game-settlers-supplement?srsltid=AYCX9vJKBFpgfWANod1j--WiP8TOcjlLrgARtUs2mXWxhi2zryWjR5J8) later. ## Pros and Cons of Each Game This side-by-side comparison helps you match each game to your group’s play style before buying a starter set or core rulebook. For your first 2d20 game, weigh genre, rules complexity, and how your group likes to play. Game Best fit and strengths Main limitation Star Trek Adventures Second Edition Groups that enjoy teamwork, clear mission goals, diplomacy, and exploration, backed by a clear Momentum and Threat economy. Starship operations, extended tasks, Determination, and different conflict modes mean more procedures to learn. Dune: Adventures in the Imperium Groups that enjoy political leverage, faction stakes, and House-level intrigue, with structured rules for social conflicts. Players need to learn the setting’s concepts and political relationships to work toward indirect goals. Fallout: The Roleplaying Game Groups that enjoy exploration, varied character options, and gear-driven action where supply choices matter. Gear tracking, survival rules, and detailed combat add bookkeeping and can slow encounters. ## Choose Your First Modiphius 2d20 Game Match your group’s preferred tone and play style to a first 2d20 game with this chart. Game Ideal group Rules emphasis Learning curve Start with Decision Star Trek Adventures Second Edition Groups that enjoy collaborative missions Crew roles, starship operations, investigation, Momentum, and Threat Moderate; guided starter play helps Star Trek Adventures Second Edition Starter Set or Star Trek Adventures Second Edition Core Rulebook Best first 2d20 game for a mix of mission types. Dune: Adventures in the Imperium Experienced roleplayers who enjoy intrigue House interests, social conflict, schemes, and narrative positioning Moderate to high; an experienced GM helps [Agents of Dune Deluxe Starter Set](https://modiphius.net/en-us/products/dune-agents-of-dune?srsltid=AYCX9vJSYs5RM4bpcj-Ov7PudPd5pYAm1d_sFTI7CI_XvLsxNuYppBZb) or Dune: Adventures in the Imperium Core Rulebook Best for political storytelling and planning your next move. Fallout: The Roleplaying Game New or experienced groups that enjoy gear-driven action Equipment, Perks, ammunition, scavenging, and combat Moderate to high; tracking gear and resources adds bookkeeping Fallout Starter Set or Fallout: The Roleplaying Game Core Rulebook Best for survival play built around loot and resource choices. Choose the setting your group wants to play - not the shortest rulebook. These games share an engine, but they support very different play styles. Start with the matching book and keep your first session focused on basic tests. Before your first session: - Choose one edition. Don’t mix books unless compatibility is explicitly confirmed, and get the matching core rulebook or starter set. - Have at least two d20s per player, character sheets, any ship or faction sheets, and trackers for Momentum, Threat, Determination, or equivalent resources. - Use pregenerated characters if your group wants to learn through play. - Learn basic tests first: identify the relevant ratings, set the Difficulty, roll two d20s, and count successes. Then apply the game’s resource rules. - Introduce starship actions, faction schemes, crafting, or settlement rules after the group understands ordinary tests. ## FAQs ### Can I enjoy these games without knowing the setting? Yes, you can enjoy these games without knowing the setting first. Even in adaptations like Fallout: The Roleplaying Game, the 2d20 system lets players bring the world to life through their actions and roleplaying. [Resource management](/category/resource-management) and skill tests give both new and experienced players a clear structure for play. You don’t need to have played the original video games or read the source material. ### Can a failed 2d20 test still generate Momentum? A failed 2d20 test typically doesn’t generate Momentum. You earn Momentum by rolling more successes than the task requires. If you fail, you haven’t met that requirement, so there are no extra successes to turn into Momentum. ### How much preparation does a first-time GM need? Prep time depends on how complex the game is - and which 2d20 game you choose. Simpler, story-driven games may take less than an hour to prepare, while games with more rules and mechanics may need 2–3 hours or longer. Pre-made adventures, character templates, and starter sets can cut your prep work by giving you the basics to get started. {"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"Can I enjoy these games without knowing the setting?","acceptedAnswer":{"@type":"Answer","text":"Yes, you can enjoy these games without knowing the setting first. Even in adaptations like Fallout: The Roleplaying Game, the 2d20 system lets players bring the world to life through their actions and roleplaying. Resource management and skill tests give both new and experienced players a clear structure for play. You don’t need to have played the original video games or read the source material."}},{"@type":"Question","name":"Can a failed 2d20 test still generate Momentum?","acceptedAnswer":{"@type":"Answer","text":"A failed 2d20 test typically doesn’t generate Momentum. You earn Momentum by rolling more successes than the task requires. If you fail, you haven’t met that requirement, so there are no extra successes to turn into Momentum."}},{"@type":"Question","name":"How much preparation does a first-time GM need?","acceptedAnswer":{"@type":"Answer","text":"Prep time depends on how complex the game is - and which 2d20 game you choose. Simpler, story-driven games may take less than an hour to prepare, while games with more rules and mechanics may need 2–3 hours or longer. Pre-made adventures, character templates, and starter sets can cut your prep work by giving you the basics to get started."}}]}