I might just be acting stupid but this causes everything in obstacleGroup and cloudGroup to go to the top left corner but ground is still in the same place.

speedIncrease = Math.round(score / 1000);
    if(speedIncrease == 1 || speedIncrease > 1){
      obstacleGroup.setVelocityXEach(obstacleGroup.velocityXEach -= speedIncrease);
      cloudGroup.setVelocityXEach(cloudGroup.velocityXEach -= speedIncrease);
      ground.velocityX = (ground.velocityX -= speedIncrease);
    }