This code creates a basic top-down alien shooter using Phaser. It includes player movement with WASD keys, aiming, and firing at waves of advancing aliens. The game also features health, score, and increasing difficulty. All graphics are procedurally generated, and no external image or audio assets are used. Please note that this is a simplified example and you may want to add more features, levels, and complexity to your game. Also, the alien image is generated using a base64 encoded string, which is a simple 1x1 pixel image. You may want to replace this with a more complex procedurally generated image. The game logic, such as aiming, firing, and increasing difficulty, is not fully implemented in this example. You will need to add this logic yourself to create a fully functional game.