How do I make enemies pass through some projectiles but not others?

[PeceMan]

I'm making custom monsters, and they're all going to be pretty projectile intensive. The thing is, I don't want them to infight. There is just going to be too many projectiles on screen, and to many monsters, so a monster hitting another one is pretty much guaranteed. So I don't want the enemies taking damage from each other, or even blocking each others bullets. 

But I also want to add some projectile weapons for the player, but those SHOULD be able to collide. So I can't just make the monsters have no collision box.

 

This is probably another one of those problems with an easy solution, but I may be wrong.

[StalkerBlade]

Give your custom monster and projectile matching species properties.

Actor MyCustomMonster 6666
{
species "MyCustomMonsterSpecies"
//etc...
}

Actor MyCustomProjectile
{
species "MyCustomMonsterSpecies"
//etc...
}

Then give the projectile the +thruspecies flag.

Actor MyCustomProjectile
{
species "MyCustomMonsterSpecies"
+thruspecies
//etc...
}

If you want the projectiles to collide with the monsters without damaging, use +donthurtspecies instead.