public void spawnEnemies() {
        if (enemies.isEmpty()) {
            for (int i = 0; i < difficulty; ) {
                int temp = rnd.nextInt(200);
                if (temp < 110 - difficulty*3) {
                    temp = 1;
                } else if (temp < 180 - difficulty*3 && temp > 110 - difficulty*3) {
                    temp = 2;
                } else if (temp >= 180 - difficulty*3) {
                    temp = 3;
                }

                Enemy e = new Enemy();
                e.setEnemy(temp);
                if (difficulty - i >= e.value) {
                    enemies.add(e);
                    i += e.value;
                }
            }
            difficulty += 3;
            level += 1;
            if (level % 4 == 0){
                currentBackground++;
            }
        }
    }