Custom Spell Impacts

Overview

Custom spell impacts allow you to create unique spell behaviors beyond the standard Spell Engine impacts. The More RPG Library provides 14 custom impact handlers that can be used in your spell.json files.

Usage

Add custom impacts to your spell.json file using this format:

spell.json

"impacts": [
  {
    "action": {
      "type": "CUSTOM",
      "custom": {
        "intent": "HARMFUL",
        "handler": "more_rpg_classes:knock_up_fixed"
      }
    }
  }
]

action.type

string

required

Must be set to "CUSTOM" for custom impacts

action.custom.intent

string

required

The intent of the impact. Can be "HARMFUL" or "HELPFUL"

action.custom.handler

string

required

The identifier of the custom impact handler (see list below)

Available Impact Handlers

Movement & Mobility Impacts

knock_up

Handler ID: more_rpg_classes:knock_up Knocks the target upward with power scaling based on spell tier and spell power. Behavior:

Calculates knock amount: base + (multiplier * spellTier * power)
Capped at configurable maximum
Applies slow falling effect for 1 second
Resets vertical velocity before applying knockup

Source: KnockUpSpellImpact.java:15

Example Usage

{
  "action": {
    "type": "CUSTOM",
    "custom": {
      "intent": "HARMFUL",
      "handler": "more_rpg_classes:knock_up"
    }
  }
}

knock_up_fixed

Handler ID: more_rpg_classes:knock_up_fixed Knocks the target upward with a fixed height (0.75 Y-velocity by default). Behavior:

Fixed upward velocity from config
Applies slow falling effect for 1 second
Resets vertical velocity before applying knockup
Does not scale with spell power

Source: KnockUpFixedSpellImpact.java:15

forward_dash_range

Handler ID: more_rpg_classes:forward_dash_range Dashes the caster forward based on the spell’s range value. Behavior:

Dash strength: spell.range / 4
Maintains or applies minimum upward velocity (0.25)
Direction based on caster’s look vector

Source: ForwardDashRangeSpellImpact.java:12

Example Usage

{
  "range": 20,
  "impacts": [
    {
      "action": {
        "type": "CUSTOM",
        "custom": {
          "intent": "HELPFUL",
          "handler": "more_rpg_classes:forward_dash_range"
        }
      }
    }
  ]
}

backward_dash_fixed

Handler ID: more_rpg_classes:backward_dash_fixed Dashes the caster backward with fixed range and height values. Behavior:

Uses configurable speed and height values
Direction opposite to caster’s look vector
Applies both horizontal and vertical velocity

Source: BackwardDashFixedSpellImpact.java:13

backward_dash_range

Handler ID: more_rpg_classes:backward_dash_range Dashes the caster backward based on the spell’s range value. Behavior:

Dash strength: spell.range / 4
Maintains or applies minimum upward velocity (0.25)
Direction opposite to caster’s look vector

Source: BackwardDashRangeSpellImpact.java:12

rush_forward_to_target

Handler ID: more_rpg_classes:rush_forward_to_target Rapidly moves the caster to directly in front of the target. Behavior:

Calculates position 1 block in front of target
Maintains caster’s Y-coordinate
Velocity matches distance to cover
Only executes on server side

Source: RushForwardToTargetSpellImpact.java:12

Example Usage

{
  "action": {
    "type": "CUSTOM",
    "custom": {
      "intent": "HELPFUL",
      "handler": "more_rpg_classes:rush_forward_to_target"
    }
  }
}

Pull & Displacement Impacts

pull_to_caster_direct

Handler ID: more_rpg_classes:pull_to_caster_direct Pulls the target directly to 1 block in front of the caster with high speed. Behavior:

Target position: 1 block in front of caster’s look direction
Maintains target’s Y-coordinate
Speed configurable via config file
Instant displacement effect

Source: PullInToCasterDirectSpellImpact.java:14

pull_to_caster_slow

Handler ID: more_rpg_classes:pull_to_caster_slow Pulls the target slowly toward the caster. Ideal for channeled spells. Behavior:

Target position: 1 block in front of caster’s look direction
Maintains target’s Y-coordinate
Slower speed than direct variant
Speed configurable via config file

Source: PullInToCasterSlowSpellImpact.java:14

Channeled Pull Example

{
  "cast": {
    "duration": 40
  },
  "on_channel_tick": [
    {
      "action": {
        "type": "CUSTOM",
        "custom": {
          "intent": "HARMFUL",
          "handler": "more_rpg_classes:pull_to_caster_slow"
        }
      }
    }
  ]
}

Knockback & Force Impacts

range_scaled_knockback

Handler ID: more_rpg_classes:range_scaled_knockback Applies knockback that increases the closer the target is to the caster. Behavior:

Knockback formula: 0.1 + ((range - distance) / 5) + enchantment_power
Considers Punch and Knockback enchantments from caster’s main hand
Higher knockback at close range
Distance calculated using block positions

Source: KnockbackRangeScaledSpellImpact.java:14

trembling

Handler ID: more_rpg_classes:trembling Throws the target in random directions. Only affects grounded entities. Behavior:

Random horizontal velocity within configured range
Fixed upward velocity (0.2)
Only applies to targets on the ground
Adds to existing velocity

Source: TremblingImpact.java:13

Example Usage

{
  "action": {
    "type": "CUSTOM",
    "custom": {
      "intent": "HARMFUL",
      "handler": "more_rpg_classes:trembling"
    }
  }
}

Utility Impacts

stop_arrows

Handler ID: more_rpg_classes:stop_arrows Stops all arrows within range by setting their velocity to zero. Behavior:

Detection range: spell.range * 1.5
Creates box: full width/depth, reduced height (range/3)
Affects all PersistentProjectileEntity instances
Sets velocity to zero

Source: StopArrowsImpact.java:14

Arrow Defense Example

{
  "range": 10,
  "impacts": [
    {
      "action": {
        "type": "CUSTOM",
        "custom": {
          "intent": "HELPFUL",
          "handler": "more_rpg_classes:stop_arrows"
        }
      }
    }
  ]
}

Environmental Impacts

lightning

Handler ID: more_rpg_classes:lightning Summons a friendly lightning entity at the target’s position. Behavior:

Spawns FriendlyLightningEntity
Won’t damage allies
Won’t set fire to blocks
Visual and audio lightning effects
Server-side only

Source: LightningStrikeImpact.java:14

Damage Impacts

damage_according_to_missing_health

Handler ID: more_rpg_classes:damage_according_to_missing_health Deals damage based on the target’s missing health percentage. Behavior:

Above 50% health: 0.25x damage multiplier
25-50% health: 1.0x damage multiplier
Below 25% health: 1.75x damage multiplier
Base damage: caster’s spell school attribute value
Final damage: schoolAttributeValue * damageMultiplier
Resets health regeneration timer

Source: DamageToMissingHealthSpellImpact.java:13

Execute-Style Spell

{
  "school": "spell_power:arcane",
  "impacts": [
    {
      "action": {
        "type": "CUSTOM",
        "custom": {
          "intent": "HARMFUL",
          "handler": "more_rpg_classes:damage_according_to_missing_health"
        }
      }
    }
  ]
}

Status Effect Impacts

frozen_ticks

Handler ID: more_rpg_classes:frozen_ticks Adds 40 frozen ticks to the target, stacking with existing freeze. Behavior:

Adds 40 frozen ticks
Stacks with existing freeze ticks
Uses custom freeze stack method
Only affects LivingEntity targets

Source: FrozenTicksSpellImpact.java:13

Implementation Reference

All custom impacts are registered in CustomSpellImpacts.java:11 during mod initialization:

Registration Example

public static void registerCustomImpacts(){
    SpellHandlers.registerCustomImpact(
        Identifier.of(MOD_ID, "knock_up"),
        new KnockUpSpellImpact()
    );
    // ... additional registrations
}

Configuration

Many impacts use configurable values from MRPGCMod.tweaksConfig.value:

Knock up base, multiplier, and cap
Pull speeds (direct and slow)
Dash ranges and heights
Trembling range
Missing health damage multipliers

These can be adjusted in the mod’s config file without code changes.

Notes

Most movement-based impacts only execute on the server side to prevent desync issues.

Impacts that modify velocity set both velocityModified and sometimes velocityDirty flags to ensure proper synchronization.

Combine multiple impacts in a single spell for complex behaviors. For example, use knock_up followed by a damage impact for a juggle combo.

API Overview

Spell System

Effects & Attributes

Loot System

Data Generation

World Generation

Overview

Usage

Available Impact Handlers

Movement & Mobility Impacts

knock_up

knock_up_fixed

forward_dash_range

backward_dash_fixed

backward_dash_range

rush_forward_to_target

Pull & Displacement Impacts

pull_to_caster_direct

pull_to_caster_slow

Knockback & Force Impacts

range_scaled_knockback

trembling

Utility Impacts

stop_arrows

Environmental Impacts

lightning

Damage Impacts

damage_according_to_missing_health

Status Effect Impacts

frozen_ticks

Implementation Reference

Configuration

Notes

Build docs developers (and LLMs) love

API Overview

Spell System

Effects & Attributes

Loot System

Data Generation

World Generation

Documentation Index

​Overview

​Usage

​Available Impact Handlers

​Movement & Mobility Impacts

​knock_up

​knock_up_fixed

​forward_dash_range

​backward_dash_fixed

​backward_dash_range

​rush_forward_to_target

​Pull & Displacement Impacts

​pull_to_caster_direct

​pull_to_caster_slow

​Knockback & Force Impacts

​range_scaled_knockback

​trembling

​Utility Impacts

​stop_arrows

​Environmental Impacts

​lightning

​Damage Impacts

​damage_according_to_missing_health

​Status Effect Impacts

​frozen_ticks

​Implementation Reference

​Configuration

​Notes

Build docs developers (and LLMs) love

Overview

Usage

Available Impact Handlers

Movement & Mobility Impacts

knock_up

knock_up_fixed

forward_dash_range

backward_dash_fixed

backward_dash_range

rush_forward_to_target

Pull & Displacement Impacts

pull_to_caster_direct

pull_to_caster_slow

Knockback & Force Impacts

range_scaled_knockback

trembling

Utility Impacts

stop_arrows

Environmental Impacts

lightning

Damage Impacts

damage_according_to_missing_health

Status Effect Impacts

frozen_ticks

Implementation Reference

Configuration

Notes