Diagnosis - Bat Bullet Patterns

Right, so the bats run this bullet-firing code every so often.

var loop,_i;
for(loop=0; loop<360; loop+=45) //fire 8 bullets at 45 degree intervals
{
    _i = instance_create(x, y, oEnemyBulletWiggle);
    _i.direction = loop + sin(degtorad(time)) * 45;
}

The bullets themselves (oEnemyBulletWiggle) run this every frame:

time += 1;
direction += cos(degtorad(time)) * amount;

So the initial direction of the bullet is a function of sin(time) while the change in direction over time is a function of cos(time).  With this system, each bullet fires just a little bit off course, in a systematic way, so as to prevent any "safe" spots.