Build a 3D RPG with Unity MCP: Third-Person Control, Combat, and Quests

A demo-ready 3D RPG prototype usually needs these pieces first: tunable third-person move and camera, one real-time melee loop, one enemy with a small state machine, one triggerable quest or dialogue, and a HUD that shows health or quest progress. This guide follows that build order. Assume you drive an open Unity project from Cursor, Claude Code, Codex, or another MCP-capable AI IDE through Unity MCP—reading and writing scenes, GameObjects, and C#, not only pasting files onto disk.

Install and connect: Unity MCP install guide. Supported editor versions follow the product page (commonly Unity 2022.3+ / Unity 6).

Scope a minimum playable slice

Ship v1 only if you can accept:

1. WASD move, mouse look, jump; ground and gentle slopes feel stable
2. One melee attack (placeholder anim OK) that hits a collider and deals damage
3. One enemy: patrol → detect player → chase / attack; disable or destroy on death
4. One NPC: approach to talk or accept a quest; objective “defeat that enemy,” then update the log
5. Simple HUD: health bar + one quest line

Block out art with primitives if needed. Treat main menu, inventory grids, polished HUD as a later UI pass (see below).

Project and MCP readiness

Before gameplay prompts:

• Unity project open; target scene can enter Play
• Unity MCP Server running; the AI IDE can list Hierarchy roots (read-only smoke)
• Baseline commit done; commit again before large edits

Read-only check:

List root GameObjects in the active scene. Do not change anything.

Only then write. Keep the bridge on localhost—do not expose the port publicly. Prompt craft: Unity MCP with Claude Code and Cursor.

Player: third-person control first

Minimal skeleton (rename to match your project):

Player
├── CharacterController or Rigidbody + CapsuleCollider
├── CameraPivot (yaw)
│   └── CameraArm (pitch) → Main Camera
└── AttackHitbox (trigger, off by default)

Be explicit about input, camera, and paths:

Create Assets/Scripts/Player/PlayerController.cs: third-person; WASD relative to camera forward; mouse yaw/pitch (pitch clamp −30°–60°); Space to jump; attach to Player. Ground via CharacterController.isGrounded or equivalent.

Then tune feel:

Move speed ~5 with light acceleration smoothing; jump ~1.2 m; slight camera follow damping—no whip-pan.

Review slopes, air steer, and camera clipping before celebrating “script generated.”

Combat: one acceptable melee loop

Skip skill trees in v1. Goal: press attack → enable hitbox for N frames → damage → refresh HUD.

Add PlayerCombat.cs: LMB attack, 0.6 s cooldown; enable AttackHitbox during the window; deal 15 damage to IDamageable. Enemies implement IDamageable and current HP.

Optional still-simple upgrades:

Lock movement briefly on attack; short hitstun on enemies; 0.4 s i-frames with blink after player damage.

Raise health changes as events/callbacks so HUD binding stays clean—avoid UI scripts Find-ing the world.

Enemies: Idle / Patrol / Chase / Attack

No behavior tree required. Four states cover a field mob:

Idle → Patrol → Chase → Attack
         ↑________________↓ (lost target)

Create Assets/Scripts/Enemy/EnemyAI.cs: two-point patrol; enter Chase within 12 m; Attack within 2 m (1.2 s cooldown, 8 damage); return to Patrol 3 s after losing the player; on 0 HP play death or SetActive(false).

Prefer NavMeshAgent if you already bake; otherwise simple seek/face motion so week one is not blocked on navigation. Animator optional—facing and color feedback are enough early.

Quests and NPCs: one mainline thread

“Quest feel” is trigger → track → complete, not a full quest editor.

Keep data plain:

• QuestId, title, description, progress count, completed flag
• NPC Interact (E or trigger) opens dialogue and StartQuest
• Enemy death calls QuestManager.NotifyKill(enemyId)

Create a QuestManager singleton: accept slay_wolf_01 (defeat 1 Wolf); advance on Wolf death; update quest log copy when done. Wizard NPC: player enters trigger, press E to start that quest.

TMP/Text is fine for v1 dialogue; branches later.

HUD: placeholders first, polished UI later

While gameplay is unfinished, wire engine Slider / TMP_Text:

Bind player OnHealthChanged to the HUD bar; bind QuestManager current title to a top-screen TMP line.

When menus, inventory, or skill bars need design-grade UI (layered PSD/Figma, NL-generated panels, split and export as Unity prefabs), use a canvas workflow such as AI Studio:

1. Generate or import RPG HUD / menu
2. Componentize and export to e.g. Assets/UI/
3. Return to the AI IDE + Unity MCP to bind buttons, bars, and quest text to existing gameplay events

Handle hard cutouts for alpha first if needed. Structure can come from the canvas; bindings and combat logic stay in Unity via MCP—do not expect the canvas tool to author a full combat FSM.

Import detail: Figma to Unity UI.

Suggested build order

MCP: player control → one melee loop → one enemy FSM → one quest + NPC
        ↓
MCP: placeholder HUD wiring (HP / quest line)
        ↓ (optional)
Canvas tool: polished menu / HUD → export to Unity
        ↓
MCP: bind polished UI to existing events

Feel, numbers, AI, navigation → keep using Unity MCP.
Full-screen visual hierarchy, reskins, re-exported prefabs → return to the canvas tool.

Prompt boundaries that actually help

Vague prompts waste cycles. Pin:

• Paths and attach points — which folder, which object
• Acceptance — e.g. “within 10 s of Play, kill one wolf and see quest complete”
• Out of scope — e.g. “do not rebuild the whole input stack; do not delete the camera”
• One concern per prompt — control, then combat, then enemy

Always Play-test yourself. MCP removes repetitive clicking; it does not replace design judgment.

Acceptance checklist

• Third-person move/camera stays controllable for ~2 minutes without obvious clipping/loss of control
• Melee hits reliably; cooldown is noticeable
• Patrol vs chase is readable; death has clear feedback
• Quest can be accepted and completed; HUD copy updates
• Health changes reach the UI (placeholders OK)

Next steps

1. Finish the Unity MCP install guide and a read-only smoke test
2. Ship “movement + one enemy + one quest” in that order
3. Add polished UI export only when the HUD must look finished