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Tutorials

Creating Your First MMO Boss

This tutorial walks through creating a fully functional MMO dungeon boss with threat management, leash prevention, party scaling, and faction-based aggro. By the end, you will have a boss NPC that:

  • Maintains a threat table and targets the highest-threat player
  • Cannot be leashed (boss fights should not reset from kiting)
  • Scales HP and damage based on difficulty tier and party size
  • Only aggros hostile faction players
  • Uses GAS abilities during combat (optional)

Prerequisites

  • FWAISystem installed and enabled
  • A Character Blueprint for your boss (e.g., BP_LichKing)
  • An AI Controller Blueprint assigned to your boss
  • Basic familiarity with Behavior Trees

Optional:

  • FWFactionSystem for faction aggro gating
  • FWGASSystem for ability activation

Step 1: Create the NPC Definition

Create a data asset for the Lich King boss:

  1. Content Browser: right-click > Miscellaneous > Data Asset > FWNpcDefinition.
  2. Name it DA_LichKing.
  3. Configure as follows:
Field Value
NpcId LichKing
DisplayName The Lich King
Category Boss
NpcClass BP_LichKing
Field Value
BehaviorTree BT_LichKing (create in next step)
PatrolMode None
AggroRadius 2500
Field Value
bCanLeash false
Field Value
ThreatDecayRate 1.0 (slow decay for boss fights)
TauntThreatMultiplier 2.0 (strong taunts for tank role)
Field Value
BaseLevel 50
AbilityTags Ability.Boss.LichKing.Frost, Ability.Boss.LichKing.Shadow

Add entries to the TierScaling map:

Normal:

Field Value
HpMultiplier 1.0
DamageMultiplier 1.0
XpMultiplier 1.0
ExpectedPlayerCount 5
PerPlayerHpScale 0.15
PerPlayerDamageScale 0.05

Hard:

Field Value
HpMultiplier 2.5
DamageMultiplier 1.8
XpMultiplier 2.0
ExpectedPlayerCount 5
PerPlayerHpScale 0.2
PerPlayerDamageScale 0.08

Mythic:

Field Value
HpMultiplier 5.0
DamageMultiplier 3.0
XpMultiplier 4.0
ExpectedPlayerCount 5
PerPlayerHpScale 0.25
PerPlayerDamageScale 0.1
Field Value
DefaultFactionId Undead
Field Value
RespawnTime 600 (10 minutes)
MaxActiveInstances 1

Step 2: Set Up Components on the Boss

Open BP_LichKing and add the following components:

  1. FW Threat Component -- Configure:

    • MaxThreatEntries: 40 (supports large raids)
    • ProximityThreatRadius: 0 (boss does not proximity aggro; controlled by perception)

  2. FW Leash Component -- Configure:

    • bCanLeash: false (boss cannot leash)

Definition Overrides

The AFWNpcSpawnPoint will automatically apply DA_LichKing's threat and leash settings to these components when the NPC spawns. You only need to set defaults here for testing without a spawn point.

Step 3: Build the Behavior Tree

Create BT_LichKing with this structure:

Root
  Selector
    |
    +-- Sequence [Decorator: HasThreat]
    |     +-- Service: UpdateThreat
    |     |     TargetActorKey: TargetActor
    |     |     HasThreatKey: bHasThreat
    |     +-- Selector
    |           |
    |           +-- Sequence [Decorator: FactionAttitude (Hostile)]
    |           |     +-- Task: FindThreatTarget
    |           |     |     TargetActorKey: TargetActor
    |           |     +-- Task: PlayAbility
    |           |     |     AbilityTag: Ability.Boss.LichKing.Frost
    |           |     |     bWaitForEnd: true
    |           |     +-- Task: MoveToTarget
    |           |           TargetActorKey: TargetActor
    |           |           AcceptanceRadius: 150
    |           |
    |           +-- Task: FindThreatTarget
    |                 TargetActorKey: TargetActor
    |
    +-- Task: Wait (5 seconds, idle)

Ability Rotation

For more complex boss fights, use a Sequence of multiple PlayAbility tasks with different cooldown decorators to create an ability rotation. The boss will cycle through abilities while chasing the highest-threat target.

Step 4: Apply Scaling at Runtime

When the dungeon instance initializes, apply scaling based on the difficulty tier and party size:

Event: On Dungeon Initialized
  |
  Get Tier Multipliers (DifficultyTier)
    |
    Compute Party Scaling (PartySize, TierConfig)
      |
      For Each Loop (BossActors)
        |
        Apply Scaling To NPC (BossActor, ScaledConfig)

void AMyDungeonGameMode::InitializeBoss(AActor* Boss, EFWDifficultyTier Tier, int32 PartySize)
{
    FFWInstanceScalingConfig BaseConfig = UFWInstanceScalingLibrary::GetTierMultipliers(Tier);
    FFWInstanceScalingConfig ScaledConfig = UFWInstanceScalingLibrary::ComputePartyScaling(PartySize, BaseConfig);
    UFWInstanceScalingLibrary::ApplyScalingToNpc(Boss, ScaledConfig);
}

Step 5: Place the Spawn Point

  1. In your dungeon level, place an AFWNpcSpawnPoint.
  2. Set NpcDefinition to DA_LichKing.
  3. Set bSpawnOnBeginPlay to false (boss spawns on dungeon trigger, not level load).
  4. Set RespawnTime to 0 (use definition default of 600 seconds).

Trigger spawning from your dungeon logic:

// When players enter the boss room
AFWNpcSpawnPoint* BossSpawn = FindBossSpawnPoint();
APawn* Boss = BossSpawn->SpawnNpc();

// Apply scaling
InitializeBoss(Boss, CurrentDifficultyTier, PartyMembers.Num());

Step 6: Listen to Threat Events

Connect to threat events for boss-specific mechanics:

Event BeginPlay
  |
  Get Component by Class (FW Threat Component)
  |
  Bind Event to On New Highest Threat
    -> Custom Event "OnTankSwap"
         |
         Print String: "New tank: " + NewTarget.GetDisplayName()
         // Trigger tank-swap mechanic

void ALichKingCharacter::BeginPlay()
{
    Super::BeginPlay();

    if (UFWThreatComponent* ThreatComp = FindComponentByClass<UFWThreatComponent>())
    {
        ThreatComp->OnNewHighestThreat.AddDynamic(this, &ALichKingCharacter::OnTankSwap);
        ThreatComp->OnThreatTableEmpty.AddDynamic(this, &ALichKingCharacter::OnEvade);
    }
}

void ALichKingCharacter::OnTankSwap(AActor* NewTarget)
{
    // Trigger tank-swap debuff mechanic
    UE_LOG(LogTemp, Log, TEXT("New highest threat: %s"), *NewTarget->GetName());
}

void ALichKingCharacter::OnEvade(void)
{
    // All players dead or out of range
    UE_LOG(LogTemp, Log, TEXT("Boss evading -- no threat targets"));
}

Step 7: Test the Boss

  1. Play in Editor with multiple player windows (or use a listen server with multiple clients).
  2. Enter the boss room to trigger the spawn.
  3. Verify:
    • Boss spawns at the spawn point
    • Boss targets the player who deals the most damage
    • Taunting transfers threat correctly
    • Boss does NOT leash when players run far away
    • Scaling applies correctly based on tier and party size
    • Boss uses abilities during combat (if FWGASSystem is present)
    • Boss resets threat when all players die

Congratulations

You now have a fully functional MMO boss with production-quality threat management, instance scaling, and faction integration. Customize the behavior tree, add more abilities, and tune the scaling parameters to match your game's balance requirements.

Next Steps