ZDoom

This is classic Doom at play. The missile spawning function can already destroy a projectile before its caller has any chance to set the owner. to something other than what it was called with. Most projectile functions require the owner as parameter - the one being used here was an exception.

Yes, I should have, but I when I was testing, I was getting right in front of the IceGuy, so I didn't notice before that it only happens at point-blank range. I'll try to be more thorough in the future.

Ah! You should have mentioned this only happens when the projectiles are fired at point-blank range. Indeed, there is something odd going on. It probably has something to do with the missile being immediately destroyed upon spawn. Unless a developer bothers to check this out soon, I'll try to remember to run some tests of my own tomorrow.

FighterPlayer damaged by IceGuyFX with IceGuyFX2
IceGuy damaged by IceGuyFX with IceGuyFX2

I tested again. For consistency's sake I used your code for eventhandler. Indeed, in some cases the source of the damage is IceGuyFX and in some cases it's IceGuy. It seems that it depends on the distance from which IceGuy shoots at you, which is why I thought that it's always IceGuyFX: I always got to the IceGuy face, so it was shooting me at point-blank range. If I get away from it, the message is like what you get. But if I get in his face, the messages are like this:

[code]
FighterPlayer damaged by IceGuyFX with IceGuyFX2
IceGuy damaged by IceGuyFX with IceGuyFX2
[/code]

class TestHandler : EventHandler
{
    override void WorldThingDamaged (WorldEvent e)
    {
        Console.Printf("%s damaged by %s with %s", GetName(e.Thing), GetName(e.DamageSource), GetName(e.Inflictor));
    }
    
    private static name GetName(Actor a)
    {
        return a == null ? 'NULL' : a.GetClassName();
    }
}

FighterPlayer damaged by IceGuy with IceGuyFX
FighterPlayer damaged by IceGuy with IceGuyFX2

I'm unable to reproduce this in GZDoom 4.5.0:

[code]class TestHandler : EventHandler
{
override void WorldThingDamaged (WorldEvent e)
{
Console.Printf("%s damaged by %s with %s", GetName(e.Thing), GetName(e.DamageSource), GetName(e.Inflictor));
}

private static name GetName(Actor a)
{
return a == null ? 'NULL' : a.GetClassName();
}
}[/code]

With IceGuy, I always get messages like:

[code]FighterPlayer damaged by IceGuy with IceGuyFX
FighterPlayer damaged by IceGuy with IceGuyFX2[/code]
It never says that player was damaged by IceGuyFX with IceGuyFX2.

They have the IceGuyFX that spawned them as their target instead of the IceGuy that launched the IceGuyFX.

Edit: I apologize, they actually have the IceGuy as their target. However, the reason why I thought they had a wrong target is because anything damaged by an IceGuyFX2 has IceGuyFX as the source of the damage instead of the IceGuy.