Last Known Location concept- how doable is this in ZDoom decorate?

[HQDefault]

So I've been thinking up some ways to implement a very basic stealth system into GZDoom. One thought that came to mind was a "Last Known Location" system.

 

So I do know that Doom's AI is pretty simple where it just walks towards a target until it finds it- I thought it might be possible to make that target an entity that is constantly tied to the Player's location as long as he's in line of sight with an enemy. Is that a thing you can do in Decorate or ACS? (I imagine the hard part would be not getting them to fire at the last known location constantly)

[Scypek2]

There seems to be something like that in Sneaky Doom! I haven't tried it out, but it seems promising.

[Mordeth]

Over at the ZDoom forums somebody made a pathfinding system for this. Of course I can't seem to find it at the moment, or I'd link it.  Basically monsters would use scripting to drop a special invisible thing at their target's location at regular intervals. In case line of sight was lost, they would go for this special thingtype instead. Their final version used ZScript to modify the normal Chase codepointer to incorporate this behaviour.  This system can then be extended to follow the exact path the player took and thus enable the monster to navigate difficult paths without its usual AI getting it stuck in dead corners.

 

With just ACS there are two main issues to solve: how to construct a sequence of path-things and when to invalidate them, and how to chase those down instead of the player without invalidating the player as its target.