Spaw enemies

GameScene.swift

// omitted
class GameScene: SKScene {
    // omitted
    var enemies = [SKSpriteNode]()
    
    override func update(delta: CFTimeInterval) {
        // loop all enemies and make then walk to collide with the player
        for enemy in enemies {
            enemy.position = CGPoint(x: Double(enemy.position.x) - 5, y: Double(enemy.position.y))
        }
        
        spawEnemy()
    }
       
    func spawEnemy(){
        // create the sprite node the red square
        let enemy = SKSpriteNode(imageNamed: "red")
        
        // define a name to the node
        enemy.name = "enemy"
        
        // define a size equal of the player
        enemy.size = CGSize(width: 50, height: 50)
        
        // define the position to be outside of the screen
        enemy.position = CGPoint(x: CGRectGetMidX(self.frame) + 350, y: CGRectGetMidY(self.frame) - 20)
        
        // create a physics body with the size of the player
        enemy.physicsBody = SKPhysicsBody(rectangleOfSize: enemy.size)
        
        // affected by gravity as the player
        enemy.physicsBody?.affectedByGravity = true
        
        // make it collide with the floor and the player
        enemy.physicsBody?.categoryBitMask = Physics.Character
        enemy.physicsBody?.collisionBitMask = Physics.Character
        
        // add the enemy to the scene
        addChild(enemy)
        
        // store the enemy to use later
        enemies.append(enemy)
    }
    // omitted
}