Introduction to the Chase Game

• In this lesson, we will create a fun chase game using Scratch, like a Tom and Jerry game.
• In this game, a mouse is the player, a cat chases the mouse, and a piece of cheese gives points to the mouse.
• If the cat touches the mouse, the game ends.
• This lesson helps students understand movement, keyboard controls, sensing, conditions, loops, variables, and scoring in Scratch.

What Students Will Learn

• How to move a sprite using arrow keys
• How to change sprite direction according to movement
• How to make another sprite chase the player
• How to detect collisions between sprites
• How to stop the game when a condition is met
• How to create and use a score variable
• How to reset positions and score when the game restarts

Adding Sprites

In this project, we will use three sprites:

• Mouse sprite as the player
• Cat sprite as the chaser
• Cheese sprite for the player to collect points

How to add sprites:

• Click on the Choose a Sprite icon at the bottom right corner
• Select a mouse sprite
• Select a cat sprite
• For the cheese, click the paintbrush icon to draw your own cheese sprite:
  • Use the line tool to draw a triangle
  • Use the eraser to create holes in the cheese
  • Click Done

Coding the Mouse Sprite (Player)

Starting the Code

• Select the mouse sprite
• Go to Events and pick when green flag clicked

Moving the Mouse with Arrow Keys

• Use if then blocks from Control to check key presses
• Sensing → key space pressed, change it to arrow keys (right, left, up, down)
• Move the sprite:
  • Right arrow: change x by 10
  • Left arrow: change x by -10
  • Up arrow: change y by 10
  • Down arrow: change y by -10
• Wrap all four if then blocks inside a forever block

Explanation: This allows the mouse to move continuously in all four directions.

Changing Mouse Direction

• Motion → point in direction
• Right arrow: 90
• Left arrow: -90
• Up arrow: 0
• Down arrow: 180

Explanation: Ensures the mouse faces the correct direction while moving.

Coding the Cheese Sprite

Gliding Randomly

• Add when green flag clicked
• Motion → glide 1 second to random position
• Put this glide block inside a forever block

Explanation: The cheese keeps moving randomly on the stage.

Eating the Cheese

• Add if then block from Control
• Sensing → touching mouse
• Looks → hide block inside the if then
• To make the cheese reappear when restarting the game, add when green flag clicked + show block

Explanation: The cheese hides when eaten and shows again at the start.

Coding the Cat Sprite (Chaser)

Chasing the Mouse

• Add when green flag clicked
• Motion → point towards mouse
• Motion → move 3 steps
• Wrap both blocks inside a forever block

Explanation: The cat continuously follows the mouse.

Game Over Condition

• Add if then block inside a forever loop
• Check touching mouse from Sensing
• Control → stop all inside the if then block

Explanation: If the cat touches the mouse, the game ends.

Setting Starting Positions

• For all three sprites, add when green flag clicked + go to x: ___ y: ___
• Place the mouse, cat, and cheese in different corners

Explanation: Ensures the game does not end immediately and sprites start from a fixed position.

Adding a Score

Creating the Score Variable

• Go to Variables → Make a Variable
• Name it score

Increasing Score

• On the cheese sprite, under the hide block, add change score by 1

Explanation: Each time the mouse eats the cheese, the score increases.

Resetting the Score

• Add when green flag clicked + set score to 0

Explanation: Resets the score at the start of each game.

Summary of What Students Learned

• How to move a sprite using arrow keys
• How to change sprite direction based on movement
• How to make a sprite chase another sprite
• How to detect collisions
• How to stop the game when a condition is met
• How to create, increase, and reset a score variable
• How to set starting positions for sprites

Task for Students

• Create your own chase game
• Choose any player and chaser sprites
• Add at least one object to collect for points
• Try adding multiple dangers, changing speeds, or adding sound effects
• Make your chase game more fun and challenging