Set Alpha Action

class Example extends Phaser.Scene
{
    constructor ()
    {
        super();
    }

    preload ()
    {
        this.load.setBaseURL('https://cdn.phaserfiles.com/v410');
        this.load.spritesheet('diamonds', 'assets/sprites/diamonds32x24x5.png', { frameWidth: 32, frameHeight: 24 });
    }

    create ()
    {
        const group = this.add.group({ key: 'diamonds', frame: 0, frameQuantity: 50, setXY: { x: 32, y: 32, stepX: 14 }});
        Phaser.Actions.SetAlpha(group.getChildren(), 0, 1 / 50);
    }
}

const config = {
    scale: { mode: Phaser.Scale.FIT },
    type: Phaser.WEBGL,
    width: 800,
    height: 600,
    backgroundColor: '#2d2d2d',
    parent: 'game-container',
    scene: Example
};

const game = new Phaser.Game(config);