Souls-like Boss Fights: Phases, an Arena and Attacks That Read the Player

Documentation Unreal Engine AI Tutorial Boss Encounters

Build an Elden Ring style boss in Unreal Engine 5: a second moveset at a health threshold, an arena that opens and ends the fight, a boss health bar, and attacks that answer what the player does, set up in Blueprint with no C++.

The player walks into the arena, the boss's health bar comes up, and the fight starts. The boss punishes a heal and parries the swing it sees coming, then opens a second moveset when its health drops. Soulslike Enemy Combat builds this from an Enemy AI Config, two Action Sets, one trigger in the level and a few Blueprint nodes.

The problem

A boss built on a plain Behavior Tree cycles a fixed list of attacks. It swings whether the player is healing or backing off, and the player learns the loop in two tries. Phases turn into a tangle of branches, and you wire the arena, the health bar and the end of the fight again by hand for every boss.

A boss feels smart when it picks each attack by what the player is doing and changes its moveset as the fight goes on. Soulslike Enemy Combat scores every attack against the situation and swaps a moveset with one node, and it ships the arena trigger and the encounter events a boss bar binds to.

You need an enemy that already attacks through an Action Set. If you have none, Getting Started builds one in a few minutes, and Step-by-Step Enemy gives it a full moveset.

Set it up

15 minutes

1
Make it the boss of the pack
Open the boss's Enemy AI Config and fill in Combat Role.
EnemyConfig_Boss
▾Combat Role
Allowed Roles (empty = any)
Priority
Ignore Target Redistribution
Elite slots are unlimited, so the boss keeps its role whatever else joins the fight.
Priority 200 gives it first pick of the roles, and Ignore Target Redistribution keeps it on the player it started on while any adds shuffle around.
2
Give it a second moveset
Create a second Action Set with the moves for the back half of the fight. In the boss Blueprint, bind On Vital Changed on its SEC Vitals component. When the Vital Tag is SEC.Vital.Health, Old Value is at or above your threshold and New Value is below it, call Set Runtime Override on the pawn's SEC Action Set Component with the phase-two set. Testing the crossing makes the swap happen once; a test on New Value alone runs it again on every later hit. The override beats every other source, the config and any weapon included.
3
Build the arena
Place BP_SEC_BossArenaTrigger from the demo's Demo/Game folder around the arena. Fill in Encounter Name and point Enemies at the boss.
The player walking in opens the fight. Once every listed enemy is dead or gone, the trigger ends it as Defeated. Untick End When Player Leaves for a fight that follows the player out of the arena.
4
Play
Press Play with the demo's player controller and walk in: the demo's encounter bar, WBP_SEC_HUD_Encounter, comes up as the fight opens. Bring the boss under the threshold and run SEC.Debug.Scoring 1; the actions listed above it are the phase-two set's.

The trigger itself puts nothing on screen. With your own player controller, add a widget that binds On Encounter Started and On Encounter Ended on the SEC Encounter Subsystem; the demo widget shows how.

Attacks that read the player

The boss scores every attack in its Action Set each time it picks a move. Tag Score Multipliers on an action multiply its score while a tag sits on the boss, on its target or on the world, so the same moveset plays differently depending on what the player does.

The player	The boss	Set this
Drinks a potion	Lunges in to punish it	On the lunge, a Tag Score Multipliers entry for the tag your heal ability puts on the player, at 3.0
Raises a guard	Reaches for its guard break and holds back its light hits	That guard tag at 2.0 on the guard break, and 0.3 on each light attack
Reels from a hit	Presses the opening	`SEC.State.Staggered` at 2.5 on a follow-up, held by a SEC State Tag Window on the player's hit reaction montage, as the counter in the parry guide reads it
Swings at the boss	Parries or dodges the blow it sees coming	A Reaction Set answering `SEC.Stimulus.AttackTelegraphed`, and a SEC Telegraph Window on the player's attack montages (Enemies That Parry, Dodge and Counter)
Keeps the camera locked on it	Swaps sides or gives ground under the stare	Tick Swap Strafe on High Threat and Adjust Distance by Threat under Threat Response on the boss's Movement Behavior Profile; both ship off (Threat Detection)
Stays out of reach	Closes the gap	A Distance Scorer whose range rewards the far band on a lunge (Action System)

The player's tags come from the ability system on the player's pawn. A heal or guard tag is one of your own project's tags, and your own abilities add it. A multiplier of 0 drops a move out of the running while its tag is present.

To stop the boss leaning on one move, set Max Consecutive Uses to 2 on it. To keep its heaviest hit out of the opening seconds, set Initial Cooldown on that action.

A scripted beat between phases

Some phase changes want a move that lands on your cue rather than the scorer's: a roar, a slam that cracks the floor. Put that action in the phase-two Action Set, with Selection set to Manual Only. It never wins a poll on its own and waits for a Blueprint to call Execute Action with its Action ID. Call it right after Set Runtime Override, on the same crossing, for a transition the player can read. Execute Action looks only in the Action Set in force, so an action left in the phase-one set is not found once the override has swapped.

Add a world tag at the same moment with Add World Tag, using a tag of your own for the phase, and give the phase-two openers that tag at 2.0 under Tag Score Multipliers. Common Patterns has the full boss recipe with every number.

A boss with adds

Adds that join the fight take turns with the boss through Combat Tokens. To let more of them swing during one phase, add an SEC Token Budget Component to the player and call Set Token Budget For This Actor when the phase opens. Enemies That Take Turns Attacking covers the group side.

End the fight your own way

A plain SEC Encounter Trigger opens the same fight and leaves the ending to you. Bind On Vital Depleted on the boss's SEC Vitals, and when it reports the health vital, call End Triggered Encounter with Defeated.

Common questions

Do I need C++? No. Every step on this page is a Data Asset, a level actor or a Blueprint node.

Can phases be StateTree states instead? Yes. Point the boss's AI Config at a StateTree and use its UpdateActionSet task to set each phase's moveset as the state starts.

Does it work in multiplayer? The boss's decisions run on the server, as every enemy's do (Multiplayer Enemy AI). The arena trigger reacts to each machine's own player, so every player's screen opens the encounter and its bar as that player walks in.

Why did it pick that attack? Run SEC.Debug.Scoring 1 to see every action's score above the boss, or open its Action Set in the Action Set Editor while the game runs and watch each card score live.

Page	Why
Common Patterns	The boss recipe with every number to type
Action System	Scoring, tag multipliers, manual actions and cooldowns
Vitals	The health pool and the events a phase swap listens to
Combat Roles	The Elite role and how the rest of the pack works around it
Enemies That Parry, Dodge and Counter	Reactions to the player's swings