ZDoom

Thanks, seems that solved this issue.

I'm not sure what you're writing, but I get the impression you want to use A_CustomMissile independently of the caller's target. CMF_AIMDIRECTION is usually required to fire when you have no monster to aim for. (As far as I know that is not a bug.)

I tried to create a monster which location is shown with a small green arrow which is attached via call to A_VileTarget. To make it work, I've created new projectile which upon spawning constantly calls A_VileTarget until the monster dies so the arrow is following the monster. I made a call to A_CustomMissile in monster Spawn state but nothing happens. I tried to guess what is wrong and noticed that monsters of this class which sees a player at level start appear to have the arrow but others don't.

I've attached an example WAD. Monsters which spawned at level load time have the pointer but others including summoned later not. Just run MAP01 and see that all replaced zombiemans are hate each other and though have valid target and A_CustomMissile fires PointerSpawner but all replaced DoomImps have not target at A_CustomMissile call time and looks like it doesn't fire any projectiles. Maybe, it's ZDoom odd treatment of CMF_CHECKTARGETDEAD which is checked any time this code pointer is called from a monster regardless of it actual value?