let ys = [];

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  // Push a new mouseY position into array every frame

  ys.push(mouseY);

  // Calculate average Y position over 150 frames

  let avgY = 0;

  for(let y of ys) {

   avgY += y; 

  }  

  avgY /= ys.length;

  // Get rid of oldest position once we pass 150

    if(ys.length > 150) ys.shift();

  // Draw a ball at average Y

  ellipse(width/2, avgY, 50, 50);

}