I don't know if this is already implemented, but in korax mod, as it is an rpg mod, korax and heresiarch should have special attacks in the old rpg fashion. The attacks for korax can be programmed in the scripts 249 through 255, and the heresiarch's could be done with a script like this:

int stall;
script 10 ( void )
{
	stall=1;
	while(stall!=0)
	{
		att=random(1,6);
		ACS_Execute(att,1,0,0,0);
		Delay(random(70,350));
	}
}

... with scripts 1 through 6 being special attacks. I have done this in a PWad I edited, and it ended up quite nicely. As you can edit the real deal, I can only suggest some attacks I've composed by using only map spots, tag conflagrations, and scripts containing projectiles, lighting effects, spawned things, and changing flats. If you're interested, or want to see any of the attacks, let me know Thanks for your attention