The user wants me to build a top-down alien shooter game using Phaser.js. Let me break down the requirements:

1. Use the pre-provided phaser.min.js (already in the current directory)
2. Top-down shooter perspective
3. WASD movement controls
4. Aim and fire at waves of advancing aliens
5. Health system
6. Score system
7. Increasing difficulty
8. Only procedurally generated graphics - no external images or audio
9. Single self-contained HTML file

Let me first check what's in the current directory to see the phaser.min.js file.

The phaser.min.js file is already present. Now I'll create a top-down alien shooter game. Let me plan the game:

1. **Player**: A procedurally drawn ship (can use graphics API to draw a shape)
2. **Movement**: WASD keys
3. **Aiming**: Mouse position determines aim direction
4. **Shooting**: Mouse click fires bullets
5. **Enemies**: Waves of aliens that advance toward the player
6. **Health**: Player has health, enemies deal damage on contact
7. **Score**: Points for killing aliens
8. **Difficulty**: Increases over time (more enemies, faster, etc.)

I'll use Phaser's Graphics object to create:
- Player ship (a triangle or spaceship shape)
- Bullets (small circles or lines)
- Aliens (various shapes/colors)
- Background (stars, space effect)

Let me write the complete game.

I've created a complete top-down alien shooter game. Let me verify the file exists and summarize what I built.