High Level Gaming has its own flavour and its own problems. In order to deal with this, the Games Master has challenges which are different from those for normal gaming. Here, I will try to show what qualities a High Level GM should have and to describe the pitfalls they may face.
The GM is a Moderator, there to facilitate or oppose the PCs' actions and plans. He may control what happens externally but must be aware that the PCs' actions will affect the global scheme which must also be interactive. The GM must sit back and allow things to develop naturally, trying not to dominate and control the game. Having said that, the GM also has an agenda to follow and should not let the PCs walk over him and give them their own way all the time. They may still have to work for their gains, must still plot and scheme, must HeroQuest against their enemies and must keep on their toes at all times. For instance, in my campaign, Brankist led an army along a Magic Road into Fort Wrath and took it from Ralzakark. He now has a long struggle to keep the Castle in the face of onslaughts from the Thanatari, Cacodemon, the Chaos in the Pits, the Poison of Dorastor and so on. He now finds that a great deal of Ralzakark's energies were spent in keeping the Chaos down in Fort Wrath and that now he has gone, Brankist must take over that Mantle. Should he sit back and se what happens, Fort Wrath will slip away and erupt in an unstoppable fountain of Chaos.
The GM must be flexible - it is very easy to continually oppose the PCs' plans and to block them at every turn. This does not make for a good game. Sometimes the PCs will have a crackpot scheme which cannot succeed in which case the GM can stamp on it hard. Otherwise, allow things to develop and grow. A scheme which fails now may spark off other events which succeed later, for instance see the Cloud Barrier of Bilini. As long as the players realise that their actions always have consequences and that they may make powerful enemies as a result of their deeds then the campaign will run smoothly.
Give players the benefit of the doubt. If something seems reasonable and could well succeed, let is succeed. Do not crush things simply because you can. Do not crush things because otherwise the Timeline will be affected. Do not rush things because they will impact adversely on other PCs. Do not crush things because they are too difficult to run.
A GM must be adaptable and able to think on his feet. This is especially important in High Level Games where politics and interaction with Heroes are involved. When a PC decides to perform a Magic Road to another Kingdom and ally the King to his cause right in the middle of a gaming session, it is no use saying "you can't do that, I haven't prepared it". If the PCs can Magic Road, allow him to do it, listen to his offer of allegiance, see what the NPC gains from it and decide, on the spot, whether it succeeds. This makes for a fast-flowing game and increases enjoyment.
The GM will be called upon to decide the outcome of HeroQuest spells and effects, how Heroic Abilities mix, how a PC petition is accepted, what effect releasing Daga onto Balazar has and so on.
The GM must be able to justify every decision he makes and must be seen to be consistent and fair. If he makes a wrong decision, he must apologise and admit he made a mistake. UNDER NO CIRCUMSTANCES allow players to "take time back" over a wrong decision - once something has been done it has been done and cannot be changed. Anything else causes Chaos and not of the Gloranthan sort. Once a GM has done this a number of times and has built up a campaign style, these things become a lot easier. With a campaign style where certain NPCs behave in a predictable way, players know what to expect from any given situation and know pretty well what is the likely outcome. If the GM keeps within these expectations then everyone should be happy. Problems occur when a GM is inconsistent and unpredictable - that is when players feel grievances. It is no use claiming that you were fair, you have to be seen to be fair and also to have the confidence of the players.
The GM must be comfortable with role-playing Heroes and Deities as well as Emperors, Kings, Runelords and peasants. At high level, PCs will interact with Heroes as equals, not as people to be feared or revered. At low-level, a Hero is as a God. At intermediate level, a Hero is, by definition, better than any PC in terms of skills, spells, abilities and status. At High Level, a Hero is just another NPC, possibly stronger or weaker than the PCs and certainly someone to interact with.
Great fun can be had by having Heroes interact directly with the PCs. Derak, for instance, lives in fear and awe of Cragspider but holds the Lord General of Death in contempt, treating him with disdain, and is an ally of Ralzakark; Solarus fears the Red Emperor, is terrified of Jar Eel, has to marry Yara Aranis and ignores the Bronze Sword Prophet. Brankist has had Harrek and Argrath killed, has allied the Bronze Sword Prophet and wants to marry the Feathered Horse Queen.
The GM should keep a note of a timeline that he wants to happen. This should indicate a projected future over the next five or ten years. He must set down what the major NPCs of the area intend to happen and how they intend to achieve their aims. In particular he must determine how different NPCs interact with each other and must have an idea of what would naturally happen if the PCs did not interfere. Once this has been achieved, the GM must determine what effects these outside activities and events have on the PCs and how the PCs can interact with outside events. For instance, from the Gloranthan Timeline, we know that the Bronze Sword Prophet leads a Pentian army against the Lunar Empire on many occasions, weakening them and drawing troops away from the Provinces and allowing Argrath to rebel successfully. This means that for the few years before these events, the Bronze Sword Prophet will be gaining in power and allies, drawing the tribes of Pent towards the Lunar Empire, stirring up trouble in the area and generally making a nuisance of the Pentian tribes. This may have no effect on the PCs unless one is involved in the security of the Lunar Empire or is a King of one of the local Client States. In my campaign, Solarus is the King of Balazar and the Elder Wilds and has a great deal to be concerned about increased Pentian aggression, especially as I have pointed out the fun to be had in a Pentian march through Balazar into the Lunar Empire and a retreat back through Balazar, giving twice the destruction. Solarus has to be concerned about the Pentian influence and has tried to limit this by allying himself with the Pentians, marrying the daughter of a Pentian Chief, becoming Count of the Marches and leader of the defences of the Empire against a Pentian attack and setting up a Temple of the Reaching Moon in Balazar. He also has tried to have his friends ally themselves with the Bronze Sword Prophet in order to deflect his attention and possibly to set the PCs up as his rivals.
In High Level Gaming, the Timeline is merely a guide to what you thought was going to happen. The PCs can change this by killing an enemy, allying an enemy, turning on their friends or doing something really unexpected. Try not to oppose them in these things, but work around them, always remembering that as the GM you can turn things to your advantage by causing their actions to have unexpected consequences though HeroQuesting or knock on effects. I generally amended the Timeline at the end of each session and completely rewrote it after two or three sessions had passed. This meant that I always had an idea of what was going to happen and could always keep an idea of consistency and fluency in the campaign - the players had the impression that something was always going to happen, which is a good thing.
To summarise, high level gaming requires the GM to be flexible, fair and imaginative to a greater extent than normal gaming. He must sit back and let the PCs drive the campaign to where they want it to go but at the same time maintaining a consistent and far-reaching background Timeline which triggers events and actions outside the PCs control to which they must react in order to regain independence. The GM must be able to role-play at all levels and must be comfortable with playing Heroes and Gods, especially as rivals and friends for the PCs. Where events change in ways that the GM has no way of expecting, he must react and let things flow to see where things end up. He may be able to influence the PCs so that they move in certain ways but must do this with subtlety and charm, not hitting them over the head with bricks all the time.
These guidelines make for a very enjoyable campaign where the PCs can progress and develop, where great fun can be had by all and where the GM is a participant in the game, almost as an extra player rather than the Boss.