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How to create spawner units for tower defense games in Scratch

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TD

TowerDefender_Alex

Posted on July 20, 2025 • Intermediate

🏰 Tower Defense Spawner Units Help

Hey everyone! I’m working on a tower defense game and need help creating spawner units that move along the track. I need to implement:

  • 🚶 Units that spawn and follow the path
  • 💥 Ram damage mechanics when units reach the end
  • 🎯 Attack system where units can shoot at enemies (like turrets)

I have the basic tower/turret code working, but I’m struggling with the spawning mechanics and making the units behave properly. Any help would be appreciated! 🙏

GD

GameDev_Master

Replied 2 hours later • ⭐ Best Answer

Great question @TowerDefender_Alex! Tower defense games have some complex mechanics. Let me break down a complete spawner unit system for you:

🏗️ Tower Defense Architecture

flowchart TD A[Game Controller] --> B[Enemy Spawner] B --> C[Enemy Units] C --> D{Path Following} D --> E[Move Along Path] D --> F[Check for Targets] F --> G[Attack System] E --> H{Reached End?} H -->|Yes| I[Ram Damage] H -->|No| J[Continue Moving] I --> K[Delete Unit] J --> D G --> L[Create Projectile] L --> M[Projectile Hits Target] style A fill:#e1f5fe style B fill:#f3e5f5 style C fill:#e8f5e8 style I fill:#ffebee style G fill:#fff3e0

🚀 Step 1: Enemy Spawner System

First, create the main spawner that generates units:

    // Main Spawner Sprite
when flag clicked
set [wave number v] to [1]
set [enemies spawned v] to [0]
set [spawn interval v] to [2]
set [enemies per wave v] to [10]

forever
if <(enemies spawned) < (enemies per wave)> then
create clone of [Enemy Unit v]
change [enemies spawned v] by [1]
wait (spawn interval) seconds
else
// Wait for wave to complete
wait until <(enemy count) = [0]>
change [wave number v] by [1]
set [enemies spawned v] to [0]
change [enemies per wave v] by [2]
set [spawn interval v] to ((spawn interval) * [0.9])
end
end

🚶 Step 2: Enemy Unit Movement

Create the enemy units that follow the path:

    // Enemy Unit Sprite
when I start as a clone
set [health v] to [100]
set [speed v] to [2]
set [ram damage v] to [10]
set [attack range v] to [80]
set [attack damage v] to [25]
change [enemy count v] by [1]

// Set starting position and direction
go to x: [-220] y: [0]  // Spawn point
point in direction [90]  // Initial direction
show

// Main movement and behavior loop
repeat until <<touching [End Point v]?> or <(health) < [1]>>
// Path following
move (speed) steps

// Check for path waypoints
if <touching [Waypoint 1 v]?> then
point in direction [0]  // Turn up
end
if <touching [Waypoint 2 v]?> then
point in direction [90]  // Turn right
end
if <touching [Waypoint 3 v]?> then
point in direction [180]  // Turn down
end

// Attack system
if <(distance to [Tower v]) < (attack range)> then
Attack Nearest Tower
end

// Check for projectile hits
if <touching [Tower Projectile v]?> then
change [health v] by [-20]
broadcast [projectile hit v]
end
end

// Handle unit death or reaching end
if <touching [End Point v]?> then
change [player lives v] by (0 - (ram damage))
broadcast [enemy reached end v]
else
change [player gold v] by [10]  // Reward for killing enemy
broadcast [enemy defeated v]
end

change [enemy count v] by [-1]
delete this clone

🎯 Step 3: Unit Attack System

Add the attack functionality to your enemy units:

    // Custom block: Attack Nearest Tower
define Attack Nearest Tower
set [nearest tower v] to [none]
set [closest distance v] to [1000]

// Find nearest tower
repeat until <(nearest tower) not = [none]>
if <(distance to [Tower v]) < (closest distance)> then
set [nearest tower v] to [Tower v]
set [closest distance v] to (distance to [Tower v])
end
end

// Attack if in range
if <(closest distance) < (attack range)> then
point towards (nearest tower)
create clone of [Enemy Projectile v]
wait [1] seconds  // Attack cooldown
end

💥 Step 4: Enemy Projectile System

Create projectiles for enemy attacks:

    // Enemy Projectile Sprite
when I start as a clone
go to [Enemy Unit v]
set [projectile speed v] to [5]
set [target x v] to (x position of [Tower v])
set [target y v] to (y position of [Tower v])

point towards x: (target x) y: (target y)

repeat until <<touching [Tower v]?> or <touching [edge v]?>>
move (projectile speed) steps
end

if <touching [Tower v]?> then
change [tower health v] by (0 - (attack damage))
broadcast [tower hit v]
end

delete this clone

🛡️ Step 5: Advanced Features

Add these enhancements for a better game:

    // Different enemy types
when I start as a clone
if <(enemy type) = [fast]> then
set [speed v] to [4]
set [health v] to [50]
set [ram damage v] to [5]
else
if <(enemy type) = [tank]> then
set [speed v] to [1]
set [health v] to [200]
set [ram damage v] to [20]
else
// Normal enemy
set [speed v] to [2]
set [health v] to [100]
set [ram damage v] to [10]
end
end

// Health bar display
forever
if <(health) < [100]> then
set [ghost v] effect to [0]
// Draw health bar above enemy
else
set [ghost v] effect to [100]  // Hide health bar when full
end
end

🎯 Key Implementation Tips

  • Use waypoints: Create invisible sprites at path corners for direction changes
  • Optimize performance: Limit the number of simultaneous enemies
  • Balance gameplay: Adjust speed, health, and damage values carefully
  • Visual feedback: Add health bars, damage numbers, and effects
  • Sound effects: Add audio for spawning, attacking, and dying

This should give you a solid foundation for your tower defense spawner system! 🏰

TD

TowerDefender_Alex

Replied 45 minutes later

@GameDev_Master This is absolutely incredible! 🤯

I never thought about using waypoints for path following - that’s so much cleaner than my previous approach. The attack system integration is perfect, and the different enemy types will make the game much more interesting.

Thank you for the complete system breakdown! This is exactly what I needed! 🙏

TP

TowerPro_Sarah

Replied 1 hour later

Excellent tutorial @GameDev_Master! 👏

For anyone building tower defense games, here are some additional gameplay elements to consider:

  • Boss enemies: Special units with unique abilities
  • Flying units: Enemies that bypass ground obstacles
  • Splitting enemies: Units that create smaller units when destroyed
  • Shield mechanics: Temporary invulnerability systems
  • Speed variations: Units that change speed based on conditions

Tower defense is one of the most rewarding game genres to develop! 🎮

VB

Vibelf_Community

Pinned Message • Moderator

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