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Mermbrain

Based on game build 714014 | Last updated: 2026-03-03

Overview​

MermBrain implements the AI decision tree for merms, governing how they interact with the world, players, and environment. It manages combat behaviors (chase, dodge, panic), tool acquisition from tool sheds, following a leader, seeking thrones during the Merm King event, assisting in garden tasks (tilling/digging), and responding to offering pot calls. The brain uses PriorityNode and WhileNode behavior trees combined with custom action functions to determine high-level actions.

It relies heavily on components such as combat, inventory, follower, timer, trader, homeseeker, childspawner, burnable, tool, and eater, as well as world-level systems like mermkingmanager.

Usage example​

-- Add MermBrain to a merm entity instance
local inst = CreateEntity()
inst:AddComponent("brain")
inst.components.brain:OnStart()

Dependencies & tags​

Components used:
burnable, childspawner, combat, container, eater, equippable, follower, homeseeker, inventory, inventoryitem, knownlocations, mermkingmanager, playercontroller, timer, tool, trader

Tags added/removed:
Adds mermprince when MermKingManager designates this entity as a throne candidate (removed upon removal/death via event listeners). No tags are added/removed in the constructor itself.

Properties​

No public properties. All internal logic is encapsulated within the behavior tree and helper functions.

Main functions​

OnStart()​

  • Description: Initializes and assigns the behavior tree (self.bt) that governs all AI decision-making for the merm. This function is called once during the entity's initialization and must be invoked for AI to function.
  • Parameters: None.
  • Returns: Nothing.
  • Error states: None. Assumes required components and world systems are available; missing components (e.g., mermkingmanager) result in degraded or safe fallback behavior within the tree.

Events & listeners​

  • Listens to:
    onremove — Removes candidate status and associated tags when the entity is removed.
    death — Removes candidate status and associated tags when the entity dies.

  • Pushes:
    merm_use_building — Fired when the merm begins using a tool shed.
    onarrivedatthrone — Fired when the merm successfully reaches a valid throne.

The onremove and death listeners are registered dynamically inside MermKingManager:ShouldGoToThrone() when an entity becomes a throne candidate. They are not directly part of MermBrain but are managed in coordination with it.