Detailed rules for new players

How the Game Works

As previously mentioned, the Arcadian Institute Roleplaying Game uses a simple d20-based system designed to keep gameplay fast, cinematic, and focused on superhero action.

Whenever your character attempts something difficult, dangerous, or uncertain, the Game Master (GM) may ask you to make a roll.

Most actions are resolved using:

1d20 + Relevant Attribute + Relevant Skill + Any Bonuses

If your total equals or exceeds the Difficulty Class (DC) set by the GM, you succeed.

The harder the task, the higher the DC.

The Core Rule

Whenever you attempt something important:

Roll:

1d20 + Modifiers

Beat the DC:

Difficulty.    DC

Very Easy.    5

Easy.           10

Moderate.     15

Difficult.       20

Very Difficult 25

Heroic           30

Legendary.     35+

Attribute Checks

Sometimes raw natural ability is enough.

In these cases, roll:

1d20 + Attribute Modifier

Examples:

  • Forcing open a door (STR)

  • Balancing on a narrow ledge (DEX)

  • Enduring poison (CON)

  • Solving a puzzle (INT)

  • Spotting an ambush (WIS)

  • Impressing a crowd (CHA)

Skill Checks

When a character has specialised training, skills are added to the roll.

Example

A student attempts to convince a crowd to evacuate.

Roll:

1d20 + CHA Modifier + Persuasion Skill

Opposed Rolls

Sometimes two characters directly compete against one another.

Both roll.

Highest result wins.

Examples:

  • Deception vs Empathy

  • Stealth vs Perception

  • Leadership vs Intimidation

  • Technology vs Technology

Combat

Combat is divided into rounds.

Each round represents roughly six seconds of action.

Every character acts in Initiative order.

Initiative

At the beginning of combat, roll:

1d20 + DEX Modifier + Bonuses

Highest result acts first.

Actions During Combat

On your turn, you may normally take:

One Action

Examples:

  • Attack

  • Use a Power

  • Assist an Ally

  • Activate Equipment

  • Perform a Special Ability

One Move

Move up to your Movement Speed.

Free Actions

Brief speech and simple interactions.

The GM determines what counts as a Free Action.

Attacking

When attacking:

Roll

1d20 + Attack Bonus

If the result equals or exceeds the target's Defence, the attack hits.

Melee Attacks

1d20 + Melee Attack Bonus

Used for:

  • Punches

  • Kicks

  • Claws

  • Weapons

  • Super Strength attacks

Ranged Attacks

1d20 + Ranged Attack Bonus

Used for:

  • Energy blasts

  • Firearms

  • Thrown objects

  • Projectile powers

Damage

When an attack hits, roll damage according to the attack, weapon, or power used.

Examples:

  • Energy Projection

  • Elemental Control

  • Weapons

  • Power Attacks

Damage reduces the target's Health.

When Health reaches 0, the character is incapacitated.

Critical Successes

A natural roll of:

Natural 20

Is a Critical Success.

Benefits may include:

  • Double damage

  • Automatic success

  • Additional effects

The GM determines the most appropriate outcome.

Critical Failures

A natural roll of:

Natural 1

Is a Critical Failure.

Something goes wrong.

The exact result is determined by the GM.

Saving Throws

Some powers and effects allow a target to resist.

The three Saving Throws are:

Fortitude

Represents physical resilience.

Used against:

  • Poison

  • Disease

  • Biological powers

  • Exhaustion

  • Environmental hazards

Formula

1d20 + Fortitude Bonus

Reflex

Represents reaction speed.

Used against:

  • Explosions

  • Area attacks

  • Falling debris

  • Speed-based effects

Formula

1d20 + Reflex Bonus

Will

Represents mental strength.

Used against:

  • Telepathy

  • Fear

  • Illusions

  • Mind control

  • Psychological attacks

Formula

1d20 + Will Bonus

Resistance

Some powers target a character's overall resilience rather than a specific Defence score.

Formula

Level + CON Modifier + WIS Modifier + Bonuses

Resistance may be used against:

  • Mutation effects

  • Environmental dangers

  • Certain special abilities

Hero Points

The GM may award Hero Points for:

  • Exceptional roleplaying

  • Heroic actions

  • Clever ideas

  • Significant story moments

Hero Points may be spent to:

  • Reroll a failed roll

  • Gain a bonus on an important check

  • Avoid certain narrative setbacks

  • Perform extraordinary feats

The exact use of Hero Points is determined by the GM.

Powers

Every mutant possesses unique powers.

Most powers require:

  • An Action to use

  • A successful attack roll or saving throw

  • Appropriate range and line of sight

Powers are organised into categories and ranks.

Higher ranks grant stronger abilities.

Teamwork

The world is full of powerful mutants.

The strongest heroes are rarely the ones who fight alone.

Players are encouraged to:

  • Work together

  • Combine powers creatively

  • Protect teammates

  • Think tactically

  • Solve problems as a group

The Arcadian Institute is built on cooperation, friendship, and growth.

The greatest victories often come from teamwork rather than raw power alone.

The Most Important Rule

These rules exist to help tell exciting stories.

Whenever a situation arises that is not covered by the rules, the GM will make a ruling that best fits the story, keeps the game moving, and ensures everyone has fun.

After all, this is a game about young mutants discovering who they are, learning to master their powers, and deciding what kind of heroes they will become.

The rules provide the framework.

You provide the story.

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