The 2d20 System
Star Trek Adventures uses the 2d20 system — a fast, flexible mechanic where you roll two twenty-sided dice and add your character's stats to determine success.
How a Skill Check Works
When your character attempts a challenging action, the Game Master asks you to make a skill check:
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Choose your Attribute and Discipline. Match the action to the most relevant Attribute (Control, Daring, Fitness, Insight, Presence, Reason) and Discipline (Command, Conn, Engineering, Security, Science, Medicine).
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Roll 2d20 + Attribute + Discipline. Add the two dice results to your relevant Attribute value and Discipline value.
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Compare to the Difficulty. The Game Master sets a Difficulty Number (DN) from 1 to 5. If your total meets or exceeds the DN, you succeed.
Example
Lieutenant Torres needs to reroute power to the shields during a firefight. The GM decides this is an Engineering (Operations) check — Reason + Engineering.
Torres has Reason 10 and Engineering 3. She rolls 2d20 and gets a 7 and a 12.
Total = 7 + 10 + 3 = 20 (first die) and 12 + 10 + 3 = 25 (second die).
The Difficulty is 3 (average). Both dice meet or exceed 3, so Torres succeeds with 2 successes.
Difficulty Levels
| Difficulty | Rating | Example |
|---|---|---|
| Routine | 1 | Performing a basic scan |
| Easy | 2 | Operating standard ship systems |
| Average | 3 | Calibrating a phaser under fire |
| Difficult | 4 | Hacking a Cardassian computer |
| Heroic | 5 | Surviving a direct torpedo hit |
Success and Momentum
Each die that meets or exceeds the Difficulty Number counts as one success.
- 1 success — You succeed.
- 2+ successes — Each extra success beyond the first generates Momentum — a shared resource the player group can spend on benefits (re-rolls, extra information, tactical advantages).
- 0 successes — You fail. The action doesn't accomplish what you intended.
Complications
If any die shows a natural 20, it generates a complication regardless of whether you succeeded. Complications introduce unexpected problems — a system overloads, an ally is endangered, the situation escalates. The Game Master decides the exact effect.
The Dice Pool
Your dice pool for any check is always:
2d20 + relevant Attribute + relevant Discipline
The Attribute and Discipline values are typically between 7 and 12 for Attributes and 1 and 5 for Disciplines at character creation. As your character advances, these values increase.
Focuses
If you have a Focus relevant to the task (an area of expertise like "Piloting" or "Xenobiology"), you add +2 to each die in your pool. This represents your deep knowledge and experience.
Summary
| Step | What to Do |
|---|---|
| 1 | GM sets Difficulty (1–5) |
| 2 | Player picks Attribute + Discipline |
| 3 | Roll 2d20 |
| 4 | Each die: d20 + Attribute + Discipline |
| 5 | Compare each die total to the Difficulty |
| 6 | Count successes; generate Momentum from extras |
| 7 | Check for natural 20s (complications) |