I've made a short video showing how to do it. Though people new to the game might like to know: https://youtu.be/zJcqsugteIk

Nightmare's a bit of a joke in Quake anyway (not counting any custom maps/campaigns where things are often deliberately more ball busting than what id originally designed). Where in Doom, the problem of enemies constantly respawning was, in fact, a nightmare, the difficulty in Quake just causes enemies to fire faster and often to their own detriment (an Ogre on Hard difficulty is more terrifying to deal with than an Ogre on Nightmare but an entire room of those bastards on Nightmare makes it seem like the forecast calls for nothing but grenades... and pain).

Copper Quake fixes Nightmare. Instead of becoming standing nade launchers, orges actually move around with low reaction time and are partially z aware.

Here's the link if anyone is interested: http://lunaran.com/copper/

It adds only minimal fixes.