Vanilla Mobs for Custom Drops

###########LivingDropHandler############
public static double rand;

    @SubscribeEvent
    public void onPassiveDrop(LivingDropsEvent event)
    {
    // you can also check the random chance here, rather than every time,
    // since you use the exact same probability for all your cases
        if (event.source.getDamageType().equals("player") && event.entity.worldObj.rand.nextFloat() < 0.2F)
        {
            if (event.entity instanceof EntityCow)
            {
                event.entityLiving.dropItem(Items.bone, 6);
                event.entityLiving.dropItem(MobDrops.cowHorn, 2);
                event.entityLiving.dropItem(MobDrops.ribCage, 1);
            }
    }
    }

##########LivingDropEvent#############
public static double rand;

    @SubscribeEvent
    public void onPassiveDrop(LivingDropsEvent event)
    {

    }
}