Create a field terrain

Principle

Adding a field terrain involves four steps:

• Add the text messages: the messages displayed on activation and end of the terrain.
• Create the effect class: the mechanical behavior of the terrain (power boost, status prevention, etc.).
• Register the terrain in the handler: link the terrain symbol to the messages.
• Trigger it: allow its activation via a move or an effect.

Adding text messages

Terrain messages are stored in file 100060 in Pokémon Studio. Two messages need to be added:

• An activation message (when the terrain appears) -- e.g., "An electric current runs across the battlefield!"
• An end message (when the terrain fades) -- e.g., "The electricity disappeared from the battlefield."

Note the line numbers of these messages in Pokémon Studio, they will be needed for registration in the handler.

Existing terrains use these line numbers in file 60:

Terrain	Activation	End
Electric Terrain	226	227
Grassy Terrain	222	223
Misty Terrain	224	225
Psychic Terrain	346	347

Creating the effect class

Terrains inherit from Battle::Effects::FieldTerrain and are placed in the 5 Battle/06 Effects/07 Field Terrain Effects/ folder.

Here is the minimum required for a working terrain:

module Battle
  module Effects
    class FieldTerrain
      class Void < FieldTerrain
        def on_end_turn_event(logic, scene, battlers)
          @internal_counter -= 1
          logic.fterrain_change_handler.fterrain_change(:none) if @internal_counter <= 0
        end
      end
      register(:void_terrain, Void)
    end
  end
end

The strict minimum is:

• on_end_turn_event: manages the terrain's duration. @internal_counter counts down remaining turns. When it reaches 0, the terrain is removed by setting it to :none. Without this method, the terrain lasts indefinitely.
• register(:void_terrain, Void): ties the symbol to the terrain via the factory pattern. Without this call, the terrain cannot be instantiated.

Between these two elements, you add the desired behavior by overriding EffectBase hooks. For example, Electric Terrain overrides on_status_prevention to prevent sleep and mod1_multiplier to boost Electric-type moves. Existing terrains in 5 Battle/06 Effects/07 Field Terrain Effects/ show the different possibilities.

affected_by_terrain?

When adding terrain-related behavior, you must check affected_by_terrain? on the target or user Pokémon. This method returns true if the Pokémon is grounded. A Pokémon is not affected if it is Flying type, has the Levitate ability, is under the effect of Magnet Rise or Telekinesis, or holds an Air Balloon.

Available hooks

Terrains can override any hook from EffectBase. The full list can be found in 5 Battle/06 Effects/100 EffectBase.rb.

Registering the terrain in the handler

The FTerrainChangeHandler manages terrain application and messages. The FTERRAIN_SYM_TO_MSG hash contains the mapping between terrain symbols and message line numbers. It is not frozen, so you can simply add entries:

module Battle
  module Logic
    class FTerrainChangeHandler
      FTERRAIN_SYM_TO_MSG[:void_terrain] = 400
      FTERRAIN_SYM_TO_MSG[:none][:void_terrain] = 401
    end
  end
end

Triggering the terrain via a move

Configure the move in Pokémon Studio

Create the move in Pokémon Studio with these properties:

• Procedure: s_terrain
• Category: Status
• PP: 10 (typical)
• Target: All Pokémon

Register the move in TerrainMove

module Battle
  class Move
    class TerrainMove
      TERRAIN_MOVES[:void_terrain] = :void_terrain
    end
  end
end

The system uses TERRAIN_MOVES[db_symbol] to find which terrain to apply. It also automatically checks whether the user holds a :terrain_extender item to extend the duration from 5 to 8 turns.

Triggering the terrain via an effect

module Battle
  module Effects
    class Ability
      class VoidSurge < ElectricSurge
        private

        def terrain_type
          return :void_terrain
        end
      end
      register(:void_surge, VoidSurge)
    end
  end
end

The effect inherits from ElectricSurge (or any existing Surge) and only overrides terrain_type. The system automatically handles the :terrain_extender item check for duration.

Reference examples can be found in 050 FieldTerrain Setting Abilities.rb.

Adding a terrain query method

module Battle
  module Effects
    class FieldTerrain
      def void?
        return @db_symbol == :void_terrain
      end
    end
  end
end

File summary

File	Action
Studio -> Battle System (file 100060)	Add activation and end messages
my-project/scripts/001 FTerrainChangeHandler.rb	Register messages in the handler
my-project/scripts/002 FieldTerrain.rb	Create the terrain effect class
my-project/scripts/003 TerrainMove.rb	Link the move to the terrain (if move)
my-project/scripts/004 Ability.rb	Create the effect (if effect)
Studio -> Moves	Create the move with s_terrain procedure (if move)

Conclusion

• First add the messages in Pokémon Studio (file 100060), as they are needed for the handler.
• Create the effect class by inheriting from FieldTerrain with at minimum on_end_turn_event and register.
• Add entries to FTERRAIN_SYM_TO_MSG to link the messages to the terrain.
• Add the entry to TERRAIN_MOVES for moves, or inherit from ElectricSurge for effects.
• Always check affected_by_terrain? before applying an effect to a Pokémon.
• Existing terrains in 5 Battle/06 Effects/07 Field Terrain Effects/ serve as reference for possible behaviors.