A complete step-by-step developer’s blueprint-including the exact prompts, plugin setup ( game-dev & game-architect), Nano Banana asset workflows, and parallel Gemini Omni 1.2 Flash video generation-deployed live to Google Cloud Run.
Yesterday, I had the opportunity to present Google Antigravity and its capabilities to a major gaming studio. While preparing, I asked myself: what’s the best way to truly showcase what it can do?
The answer was obvious — build a complete, AI-native game from scratch by combining Antigravity with Google’s multimodal models (Gemini Omni 1.2 Flash for real-time video generation and Nano Banana for consistent 3D assets).
This article is the exact blueprint and project that came out of that session.
Introduction: Why Game Development Is the Ultimate Test for Agentic AI
Building even a single polished mobile arcade game traditionally requires an entire studio pipeline:
- Creative Direction & Game Design: Core loop, lane math, difficulty curves, and reward pacing.
- 2D/3D Concept & Sprite Art: A consistent hero character, seamless environment backdrops, collectibles, obstacles, and alpha-transparent sprite sheets.
- Cinematic Video & Cutscene Production: An official launch trailer plus celebratory stage-completion cutscenes that reward players at the end of every level.
- 60fps Game Engine Engineering: Zero-garbage-collection memory pooling, high-DPI canvas scaling, perspective projection math, and responsive touch/keyboard input.
- Procedural Audio Synthesis: Multi-harmonic sound effects that respect browser Web Audio gesture policies without bloating bundle size.
- Automated QA & Cloud Deployment: Unit tests, headless browser end-to-end verification, and containerized deployment to production.
In this guide, we share the exact step-by-step setup and prompts we gave to Google Antigravity (AGY) to build Monster Rush: The Lost Island-showing how to install the game-dev plugin, enable the game-architect and image-generator (Nano Banana) subagents, and generate parallel in-game video cutscenes with Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash).
1. Watch the Gemini Omni 1.2 Flash Videos & Stage-Completion Cutscenes
Every cinematic below was generated using Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash), conditioned on our canonical Nano Banana character and environment sheets so the hero character ( Bramble) remains 100% visually consistent across gameplay and video cutscenes:
https://medium.com/media/da776bfaf60d24af876a4bf8e9c90ac1/href
Stage 1 Complete Cutscene: “Great job! You completed Stage 1!” (Direct MP4 Link)
https://medium.com/media/c2b20895ac80eede09314c73f8b025a8/href
Stage 2 Complete Cutscene: “Great job! You passed Stage 2! Let’s go to Stage 3!”
https://medium.com/media/dabc7facc3fa4c39b0281e195ac1d92a/href
2. Setting Up Google Antigravity: Plugins, Agents, and Multimodal Models
Before writing our first game design prompt, we configured our Google Antigravity environment with the specialized plugins and subagents needed for a 60fps game studio pipeline:
Step 0.1 — Installing & Enabling the game-dev Plugin (/plugin)
First, we asked Antigravity to install and enable the game-dev plugin (~/.gemini/config/plugins/game-dev) using the /plugin workflow:
Setup Prompt to Antigravity:
“Install and enable thegame-dev plugin, including the game-architect agent, the AGENTS.md zero-GC / 60fps game development rules, and the HTML5 game engine, arcade physics, and procedural Web Audio synthesizer skills."
Enabling the game-dev plugin automatically equips Antigravity with:
- The game-architect Subagent: An expert Game Architect agent specializing in game mechanics, mathematical balancing, difficulty curves, 60fps canvas performance, and multi-sensory game feel.
- Always-On Game Engineering Rules (game-dev/rules/AGENTS.md): Enforces Zero Garbage-Collection in game loops (ObjectPool reuse), High-DPI window.devicePixelRatio scaling, Web Audio gesture compliance, procedural audio synthesis, and clean separation of simulation state from rendering.
- Three Specialized Game Skills (SKILL.md): html5-game-engine, arcade-physics-and-grid-mechanics, and game-audio-synthesizer.
Step 0.2 — Enabling the image-generator Subagent (Nano Banana) & Gemini Omni 1.2 Flash
Alongside the game-dev plugin, our workflow uses two multimodal engines:
- image-generator Subagent (powered by Nano Banana): Generates the canonical 3D character sheet (Bramble), 4-panel expression poses, floating island environment backdrop, and 3D sprite sheet.
- Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash): Generates the 15-second 16:9 launch trailer and the voice-acted Stage 1 & Stage 2 completion cutscenes in parallel, anchored to the Nano Banana reference images.
3. The Complete Prompt Playbook: Step-by-Step Prompts Given to Antigravity
Below are the exact instructions and prompts we gave to Google Antigravity to build Monster Rush: The Lost Island step by step. Developers can copy and adapt this exact sequence for any game genre.
Prompt 1 — Architecture & Game Design Blueprint (Planning Before Coding)
Instead of asking the AI to write code immediately, our first prompt instructed Antigravity (guided by the game-architect agent and game-dev rules) to design the complete game concept, core loop, visual asset manifest, and technical architecture first-and wait for approval:
You are a senior game development team working on a premium-quality
casual mobile game prototype.
We are creating an original game called:
MONSTER RUSH: THE LOST ISLAND.
GAME CONCEPT:
A cute, brave little monster explores a magical floating island.
The player collects energy gems, avoids obstacles, discovers treasure,
and restores the island's magical portal.
TARGET EXPERIENCE:
A polished, highly visual casual arcade game suitable for a mobile
gaming audience.
YOUR TASK:
1. Design the complete game concept.
2. Define the core gameplay loop.
3. Design the main character and game world.
4. Define the screens, UI, scoring and progression.
5. Create a technical architecture for a playable browser-based prototype.
6. Define all visual assets we need to generate.
7. Create a step-by-step implementation plan.
IMPORTANT:
Do not start coding yet.
Do not use copyrighted characters or existing game IP.
The visual identity must be completely original.
Present the plan and wait for approval.
Prompt 2 — Generating the Canonical Character, Environment & Sprite Sheets with Nano Banana (image-generator)
Once the architecture plan was approved, we gave Antigravity a 3-part visual prompt so the image-generator subagent (Nano Banana) would establish a canonical character design first and preserve that exact visual identity across the environment and game item sheets:
Use Nano Banana (the image-generator subagent) to create our visual assets:
1. CANONICAL CHARACTER:
Create an original premium mobile game character for MONSTER RUSH: THE LOST ISLAND.
Character: A small adorable turquoise-blue fantasy monster. Large expressive amber eyes,
tiny golden horns, soft rounded body, short legs, small glowing markings, and a confident
friendly smile.
Style: High-end stylized 3D animated game art, soft cinematic lighting.
Composition: Full body, centered, three-quarter view, clean simple background.
This is the canonical character design. Preserve the exact same appearance in future assets.
2. ENVIRONMENT CONCEPT ART:
Create a premium game environment concept art for MONSTER RUSH: THE LOST ISLAND.
A magical floating island in the sky with bright turquoise waterfalls, lush green platforms,
ancient stone ruins, glowing magical crystals, floating bridges, and golden sunlight.
Clear foreground, middle ground, and background. No characters, no text, no logos.
3. CONSISTENT GAME ASSET SHEET:
Create a consistent game asset sheet matching the exact visual style and lighting:
- Golden collectible coins
- Glowing blue energy gems
- Magical treasure chest
- Stone obstacle
- Spinning wooden trap
- Magical portal
- Heart / life icon
- Game power-up icons
Arrange each asset separately with clear spacing and no overlapping assets.
Prompt 3 — Creating & Iteratively Refining the 15-Second Launch Trailer with Gemini Omni 1.2 Flash
With the canonical character and environment images saved in public/assets/, we instructed Antigravity to use Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash) with those exact reference images to produce a 15-second 16:9 launch trailer, followed by an iterative refinement prompt for the final 3 seconds:
Use Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash) to create a spectacular
15-second cinematic trailer for MONSTER RUSH: THE LOST ISLAND.
Use the supplied character and environment images as visual references.
Preserve the character's exact appearance, colors, proportions, and distinctive features.
STORYBOARD:
- Seconds 0-4: A breathtaking aerial cinematic flight over a magical floating island,
waterfalls, and ruins. The camera moves toward a glowing ancient portal.
- Seconds 4-8: Reveal our cute turquoise monster hero. The monster looks toward the
camera, smiles, and prepares to run.
- Seconds 8-12: The monster jumps across floating platforms, collects glowing energy
gems, and passes through magical golden particles.
- Seconds 12-15: A dramatic camera pullback reveals the entire island as the magical
portal lights up. End on a memorable heroic pose.
VISUAL DIRECTION & AUDIO:
Premium stylized 3D animated game trailer, vibrant colors, smooth camera movement,
energetic orchestral fantasy game music, and magical sound effects.
Format: 16:9 landscape, 15 seconds. Save to public/assets/monster_rush_trailer.mp4.
Keep the same character, environment, and visual style.
Make the final 3 seconds more spectacular: increase the magical glow of the portal,
add a beautiful energy burst, and finish with a stronger cinematic camera pullback.
Preserve the rest of the video and save it in public/assets/.
Prompt 4 — Implementing the Complete 60 fps Playable Game Engine
Next, we instructed Antigravity to implement the complete playable HTML5 Canvas game from scratch using the generated assets in public/assets/ and enforcing the game-dev plugin rules:
Now implement MONSTER RUSH: THE LOST ISLAND from scratch, using the approved
game design and the generated visual assets located in public/assets/.
BUILD A COMPLETE PLAYABLE GAME:
- Create a fun arcade-style 3-lane runner experience.
- The player can move left/right between lanes, jump, and trigger a spin-dash.
- Collect coins, glowing energy gems, and treasure chests.
- Avoid stone obstacles and spinning wooden traps.
- Add increasing speed and difficulty across stages.
- Include score, lives, combo multipliers, and collectible counters.
SCREENS:
1. Intro screen with the integrated Gemini Omni 1.2 Flash cinematic trailer.
2. Animated start screen with hero showcase.
3. Main 60fps gameplay screen.
4. Pause screen, Game-over screen, and Victory / Stage progression screens.
VISUAL & TECHNICAL QUALITY:
- Use the generated Nano Banana character, environment, and item sprites.
- Add particle bursts, floating score callouts, and camera shake feedback.
- Synthesize all game audio procedurally using the Web Audio API skill.
- Support both desktop keyboard (Arrows / WASD / Space) and mobile touch swipes.
Prompt 5 — Parallel Generation of Stage-Completion Cutscenes with Gemini Omni 1.2 Flash
When the player completes Stage 1 or Stage 2 by leaping into the awakened portal, we wanted a voice-acted celebratory video generated by Gemini Omni 1.2 Flash to play immediately before transitioning to the next stage:
Use Gemini Omni 1.2 Flash (models/gemini-omni-1.2-flash) in parallel using our
canonical Nano Banana character and environment reference images to generate
celebratory stage-completion videos that play automatically at the end of
Stage 1 and Stage 2 before moving to the next stage:
1. public/videos/stage1-complete.mp4:
When finishing Stage 1, before moving to Stage 2, play a celebratory video
where our turquoise monster hero leaps out of the awakened portal, waves
happily at the player, and says enthusiastically:
"Great job! You completed Stage 1!"
2. public/videos/stage2-complete.mp4:
When finishing Stage 2, before moving to Stage 3, play a celebratory video
with magical fireworks and an opening golden treasure chest where our hero
cheers:
"Great job! You passed Stage 2! Let's go to Stage 3!"
# Parallel Gemini Omni 1.2 Flash Video Generation with Reference Images
payload = {
"model": "models/gemini-omni-1.2-flash",
"generation_config": {"thinking_level": "high"},
"response_format": {
"type": "video",
"aspect_ratio": "16:9",
"duration": "10s",
},
"input": [
{"type": "text", "text": prompt_text},
{"type": "image", "mime_type": "image/png", "data": encode_img(CHAR_PATH)},
{"type": "image", "mime_type": "image/png", "data": encode_img(ENV_PATH)},
],
}
Prompt 6 — End-to-End Integration, Automated Browser QA & Cloud Run Deployment
Complete, verify, and deploy the Monster Rush experience:
1. Integrate the launch trailer and the Stage 1 / Stage 2 completion videos
into the game's screen flow.
2. Verify all generated assets and videos load properly.
3. Test keyboard and touch controls, gem collection, collisions, pause,
game-over, and stage transitions using unit tests and headless browser E2E tests.
4. Deploy the game live to Google Cloud Run, serve this developer guide under /docs,
and push the complete repository to GitHub.
Do not claim that something works unless it has actually been tested.
4. Deep Dive: Zero-GC Object Pooling & 3-Lane Perspective Math
Guided by the game-dev plugin rules, ObjectPool pre-allocates fixed pools of entities ( 80), particles ( 180), and floating score callouts ( 32), recycling expired items in O(1) time via swap-and-pop so the garbage collector is never triggered during gameplay:
export class ObjectPool {
constructor(factoryFn, initialSize = 64) {
this._factory = factoryFn;
this._free = [];
this.activeList = [];
for (let i = 0; i < initialSize; i++) {
this._free.push(this._factory());
}
}
acquire() {
const item = this._free.length > 0 ? this._free.pop() : this._factory();
this.activeList.push(item);
return item;
}
releaseAt(activeIndex) {
const lastIdx = this.activeList.length - 1;
const item = this.activeList[activeIndex];
if (activeIndex !== lastIdx) {
this.activeList[activeIndex] = this.activeList[lastIdx];
}
this.activeList.pop();
this._free.push(item);
}
}
5. Play the Live Game Right Here (Hosted on Google Cloud Run)
Click Here for start playing
Conclusion: Key Takeaways for Developers Building Games with Antigravity
- Install Domain Plugins First (game-dev & game-architect): Enabling the game-dev plugin gives Antigravity architectural guardrails (AGENTS.md) and specialized skills (html5-game-engine, arcade-physics-and-grid-mechanics, game-audio-synthesizer) before a single line of code is written.
- Design Before Coding (Prompt 1): Asking Antigravity to produce and validate the game design, state machine, and asset manifest first prevents architectural rework later.
- Anchor Multimodal Video Generation with Canonical Reference Images (Prompts 2 & 3): Generating a canonical character sheet first with the image-generator subagent (Nano Banana) and passing it as an image reference to models/gemini-omni-1.2-flash solves character consistency across gameplay sprites, launch trailers, and stage-clear cutscenes.
- Run Video Jobs in Parallel (Prompt 5): Dispatching all models/gemini-omni-1.2-flash video requests concurrently via ThreadPoolExecutor cuts media production latency by 3×.
- Close the Loop with Browser E2E Verification (Prompt 6): Coupling node –test unit tests with headless Chrome CDP verification guarantees that assets, videos, audio synthesis, and UI overlays work together with zero runtime errors.
Originally published at https://monster-rush-lost-island-880601596687.us-central1.run.app.
Building AI-Native Games with Google Antigravity & Gemini Omni 1.2 Flash was originally published in Google Cloud – Community on Medium, where people are continuing the conversation by highlighting and responding to this story.
Source Credit: https://medium.com/google-cloud/building-ai-native-games-with-google-antigravity-gemini-omni-1-2-flash-963b8fa81fa3?source=rss—-e52cf94d98af—4
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