Following

Is there a script to make friendly monsters follow the player in ZDooM?

zdoom doesn't have friendly monsters

You can make monsters friendly by using Thing_Hate.

thedemonsarecoming said:

You can make monsters friendly by using Thing_Hate.

Not quite, that just makes you not the target. It has nothing to do with 'friendly'.

MBF and it's decendants have Friendly/Helper AI.

What is the difference between friendly and helping you fight your enemies?

That the helper monsters from MBF/Eternity actually have a bot (albeit a very simple one) that makes them follow the player.

Friendly monsters in MBF/prBoom/Eternity/SMMU (I think that's it) will follow you around and generally just search for any monsters (while staying within a predefined radius of the player), and also they will wake up upon the start of the map. Once all the bad monsters are dead, they'll continue to follow you around. If you shoot them once, they'll shoot you once.

ZDoom's Thing_Hate special works like that to an extent. There are various options such as monster hunts for other monsters with this tid, monster only goes after monsters with the proper tid which it can see, monster totally ignores the player, and so on. If you set the monster to ignore the player then once all the monsters with the specified tid are dead he'll go back to sleep and there isn't any way to wake him up again (not even shooting him). If you're clever and perhaps place a monster with the proper tid in an inaccessable part of the map, even though he won't go back to sleep, he won't follow you around. I haven't tried it myself but I imagine they would wander the map aimlessly or get as close as possible to that inaccessable spot and hover around that general area.

If you want to see Thing_Hate in action (I haven't seen it used much since it's realtivly new) you should check out dwforums.wad (in /newstuff right now), which makes good use of it, though only one 'brand' of thing_hate was used. BTW this thread belongs in editing, which is where I'll be putting it now heh.