Advice on creating a unique wandering horde?

So I’m trying to mod in a game mode that is basically just like the movie “It Follows”, where a specific special zombie/horde is perpetually hunting down the player such that, in order to stay alive, you either have to kill it or cover a ton of ground to buy yourself the time to stay in one place for a little bit before it inevitably catches up to you. There is no permanent escape, only delay.

It seems to me the way to do this would be to use the wanderspawn horde feature to create a unique horde that is a.) perpetually aware of the player’s exact location and b.) always moving towards it at a high but still out-runnable speed while c.) starting at a reasonable but not extreme distance so you aren’t just jumped by a hulk as soon as you spawn.

Before I really go to town, I was curious if anyone has any alternate ideas or concerns about the wanderspawn approach and, if not, pointers on where I should start poking around in the code.