Design document · Rocket Mouse
Game design document
My design doc, 6 pages: controls and colour mixing, ships, enemies, bosses, the level plan and the story.
Rocket Mouse: game design document
1. Overview
- Title: Rocket Mouse
- Engine: Unity (3D project, 2D pixel-art look)
- Genre: Retro arcade vertical space shooter
- Input: Mouse only
- Length: 10 levels, difficulty rising each level
- Learning goal: teach how additive (RGB) light mixing works: three primaries, how they combine, and that all three together make white.
2. Core gameplay
Controls
| Input | Action |
|---|---|
| Move mouse | Plane follows the cursor |
| Left click | Red channel |
| Middle click | Green channel |
| Right click | Blue channel |
| Hold buttons | Charge/mix a color; the plane glows in that color |
| Release | Fire the mixed color |
| Hold all three (bar full, Level 9+) | White power move |
Color combinations
| Buttons | Color |
|---|---|
| Left | Red |
| Middle | Green |
| Right | Blue |
| Left + Middle | Yellow |
| Middle + Right | Cyan |
| Left + Right | Magenta |
| All three | White (power move only) |
There is no "no-click" color: a shot always needs at least one button.
Rules
- Matching color: the Shade bursts into light and is freed. Points are awarded, and the White bar fills (from Level 9).
- Wrong color: the Shade absorbs the shot, flashes, and speeds up briefly. The combo resets. From Level 9, a wrong shot also drains some of the White bar.
- Damage: touching a Shade or being hit by an enemy shot costs 1 heart.
- Escaped Shades: Shades that leave the bottom of the screen cost points, not hearts.
- Combo: 5 correct frees in a row gives bonus points (and extra White bar fill from Level 9).
- Stars: each level awards 1–3 stars based on accuracy and hearts remaining.
- Colors carry over: the player keeps every unlocked color, even when a ship is destroyed.
White power move (Level 9+)
- Fills from: correct frees (small amount) and combos (bonus).
- Drains from: wrong-color shots.
- Effect: a white shockwave frees every Shade on screen.
- Boss use: in Level 10, White is the only thing that breaks The Grey Heart's shield.
3. Ships
| Ship | Levels | Hearts | Speed | Fire rate | Feel |
|---|---|---|---|---|---|
| Starling (starting plane) | 1 – 5 (first half) | 3 | Medium | Medium | Reliable, balanced |
| Sparrow (small plane) | 5 (second half) – 7 | 2 | Slow | Slow | Fragile; the player feels the loss |
| Solar Wing (fast plane) | 8 – 10 | 4 | Fast | Fast | Powerful comeback |
Ship destruction in Level 5 is a scripted story event, never a fail state.
4. Enemies ("Shades")
Shades are colors corrupted by the Grey. The player frees them with their matching light.
| Enemy | Color | Buttons | Behavior | First level |
|---|---|---|---|---|
| Ember | Red | L | Dives straight down, fast | 1 |
| Moss | Green | M | Drifts slowly in a wave pattern | 2 |
| Drip | Blue | R | Moves in steps, fires slow falling drops | 3 |
| Spark | Yellow | L+M | Zigzags quickly | 4 |
| Tide | Cyan | M+R | Arrives in swarms of 4–6 | 5 |
| Wisp | Magenta | L+R | Blinks and teleports short distances | 6 |
| Prism | Shifting | Changes | Cycles color every 2 seconds; hit it in its current color | 7 |
| Knot | Mixed | Varies | Each correct part removes that channel (Yellow hit with Red leaves Green); freed when no color remains | 8 |
| Hollow | Grey shell | White, then core color | Grey shell absorbs all colors; White breaks it and reveals a colored core to hit | 9 |
5. Bosses
The Devourer (Level 5, scripted)
A giant grey void leviathan. It ambushes the Starling mid-level and destroys it. It cannot be beaten here; it is a story moment.
The Grey Heart (Level 10, final boss)
- Shell phase: releases fast waves of primary Shades (Red, Green, Blue).
- Mix phase: releases mixed Shades and Knots; its body shifts color like a Prism. Hitting it in its current color damages it.
- Core phase: a grey shield covers its core. The White power move cracks the shield, then the player hits the exposed core with the color it shows. Repeat 3 times.
6. Level plan
| # | Name | Ship | New in this level | Waves | Challenge |
|---|---|---|---|---|---|
| 1 | First Light | Starling | Tutorial + Red | 3 | Slow, one enemy at a time |
| 2 | Green Drift | Starling | Green | 4 | Two colors mixed together |
| 3 | Blue Deep | Starling | Blue | 5 | All primaries; enemy shots begin |
| 4 | Yellow Storm | Starling | Yellow (first mix) | 5 | Learning to hold two buttons |
| 5 | The Ambush | Starling → Sparrow | Crash + Cyan | 6 | Crash halfway; continue with fewer hearts |
| 6 | Limping Through | Sparrow | Magenta | 6 | All 6 colors on a weak ship |
| 7 | Shifting Skies | Sparrow | Prism enemies | 7 | Timing and color reading |
| 8 | New Wings | Solar Wing | Fast plane + Knot enemies | 7 | Speed; breaking colors apart |
| 9 | White Dawn | Solar Wing | White power bar + Hollows | 8 | Managing the power bar |
| 10 | Heart of the Star | Solar Wing | Everything | Boss | Final test |
Inside each level: the first wave is easy, middle waves get faster and mix colors, and the last wave is the hardest. End on a peak, then play the narration.
Difficulty dials: enemy speed, spawn rate, number of colors on screen at once, reaction window, enemy shots, and (from Level 9) White bar drain.
Level 1 tutorial
- "Move your mouse": fly through 3 light rings.
- "Left click to shine Red": free 3 slow Embers.
- "Match the color": only matching colors work.
- A short final wave, then the Green unlock.
Level 5: The Ambush
- First half: Starling with Red, Green, Blue and Yellow.
- Midpoint: the screen darkens, The Devourer appears, and the Starling is crushed (cutscene).
- Second half: the player flies the Sparrow. Luma finds Cyan in the salvaged core.
7. Visual progression
Early levels are almost grey. Backgrounds become more colorful as colors are freed; the ending is full color. The world shows the player's progress.
8. Narrative: Rocket Mouse and the Grey Silence
Characters
- Rocke: a young pilot from a small grey mining asteroid who has never seen real color.
- Luma: the ship's AI, living inside a glowing light core. Warm, a little funny; she narrates the story.
- The Grey: an emptiness that eats color. The Shades are colors it has corrupted.
Premise
The Great Star once lit the galaxy with pure white light. The Grey swallowed it, and its colors scattered across space, twisted into frightened monsters called Shades. Rocke finds an old plane with a strange light core inside. The core wakes up.
Story mechanic: when a ship is destroyed, Luma's core is saved and fitted into the next ship, which is why the player keeps every color.
Level 1 — First Light
Intro > Luma: "Systems online… Hello, pilot. I'm Luma. My core holds a spark of the old Star, just one color for now. Red. Let's see if you can shine it."
Outro > Luma: "Did you see that? The Shade didn't die. It remembered what it was, and went home to the sky. Wait… I'm feeling something new. Green."
Level 2 — Green Drift
Intro > Luma: "Green is the color of growing things. The Shades here are slow and sad. Be gentle, but be quick."
Outro > Rocke: "Every one we free makes the sky a little brighter." > Luma: "And makes me a little stronger. Here comes Blue."
Level 3 — Blue Deep
Intro > Luma: "Red, Green, Blue. These three are the roots of every color there is. Master them, and you can make anything."
Outro > Luma: "Pilot… I think the three colors can mix. Try holding two at once."
Level 4 — Yellow Storm
Intro > Luma: "Red and Green light together make Yellow. Strange, right? Light doesn't mix like paint. It adds."
Outro > Rocke: "Something's following us. Something big… and grey." > Luma: "Stay calm. Keep flying."
Level 5 — The Ambush
Intro > Luma: "The Grey knows we're here now. Every color we free is one it has lost."
Midpoint (crash) > Luma: "Rocke, PULL UP. It's the Devourer! Hull breaking… Eject! EJECT!" > (Silence. Darkness. Then a faint glow.) > Luma: "…Still here. I grabbed my core before the plane went. There's an old scout ship nearby, small but alive. And Rocke… the crash cracked something open in me. Cyan."
Outro > Rocke: "We lost the Starling." > Luma: "We lost a ship. We didn't lose the light."
Level 6 — Limping Through
Intro > Luma: "This little Sparrow can't take many hits. We fly smart now, not fast. And look, Red and Blue together make Magenta."
Outro > Luma: "Six colors, pilot. Only one left to find, and it isn't a color at all. It's all of them."
Level 7 — Shifting Skies
Intro > Luma: "These Shades can't decide what they are. They're changing colors, confused. Watch closely, and free them when they show their true light."
Outro > (The freed colors gather around the Sparrow, glowing.) > Luma: "Rocke… they're not leaving. They want to help."
Level 8 — New Wings
Intro > (The freed colors swirl together and form a brand-new ship.) > Luma: "The colors we saved built us wings. Meet the Solar Wing. Fast, strong, and full of light. Let's go get our Star back."
Outro > Luma: "Some Shades are knotted together now. Pull them apart one color at a time. You're ready for what's next."
Level 9 — White Dawn
Intro > Luma: "All six colors are inside me now. If I bring them together… Pilot, feel that? That's White. The light of the old Star itself. Fill the bar, then let it shine."
Outro > Luma: "The Hollows were guarding something. The Grey Heart is just ahead. That's where the Star was swallowed."
Level 10 — Heart of the Star
Intro > Rocke: "Luma, whatever happens…" > Luma: "I know. Just fly, Rocke. We finish this together."
During the boss > Phase 2 — Luma: "It's stealing colors! Match what it shows you!" > Phase 3 — Luma: "Its core is shielded. Only White can break it. NOW, Rocke!"
Ending > (The Grey Heart cracks. Pure white light pours out, and the Great Star reignites.) > Luma: "Look, Rocke. Look at all of it." > (Rocke's grey home asteroid slowly fills with color for the first time.) > Rocke: "So this is what color looks like." > Luma: "No, pilot. This is what light looks like when it's free." > > THE END
What the story teaches
- Levels 1–3: the three primaries of light.
- Level 4: light mixes by adding, unlike paint.
- Levels 5–6: the other two secondaries.
- Level 8: mixed colors can be broken back into parts.
- Level 9: all colors of light together make white.