House Rules for
The first and most useful House Rule is what I call Sensing. It allows characters to sense the presence and use of Powers such as Pattern, Logrus and magic without the need for a lens. This helped to eliminate the almost complete reliance on advanced powers that caused so much frustration in Relative Difficulties; without a lens one could discover nothing. By being able to sense powers at work or the energies left by their usage with Psyche alone, characters can investigate plots without being required to spend vast amounts of points or constantly call for assistance.
Of course, being able to sense something is still useless if you do not know what it is or what was done; a lens will frequently reveal information mere Psyche would not, simply because of the greater amount of knowledge one has by having studied to gain the ability.
The second and perhaps more important rule is the Psyche Rule. This states, very simply, that all Psyche contacts take two seconds to gain sufficient stability to become useful. The reason this exists is to counter another problem from Relative Difficulties; Psyche contacts took no time at all, and so could be used in combat.
Try and wrestle Gerard into submission? No, just get within arm's reach and fry his brain. The same went for Benedict.
Fortunately, no one actually tried either 'trick'.
By putting this delay on attaining contact it becomes possible for people to react to them; whether it be punching their assailant or breaking a Trump contact by passing a hand over it.
Another Rule related to the Psyche Rule is what I call the Rewrite Rule. This makes psychic shenanigans a much more careful and risky affair; no longer can one completely rewrite some poor mortal's mind to make them a living, homicidal 'time-bomb' and expect then to remain a normal person at the same time. The more adverse the interference (scan, deep scan and rewrite, in order of rising severity) the more damage it causes/can cause; in theory, taking great care can cause little damage on even a deep scan, while most rewrites always cause some glitches. The previously mentioned time-bomb would probably be either listless and befuddled until his time came to act or would be a jumpy psychopath itching to kill.
When the time came to act such an individual would probably become a single-minded automaton if not primed properly (made to think he was a fanatical terrorist, for example) or not combat trained. He would probably soon become a vegetable whether he ever got to act or not, due to having a terribly fractured mind (or what remains of one).
Generally, the more the original mind would resist the compulsions/rewrite, the more lobotomised the individual would become. This was done to countermand the increasing ease of plumbing the depths of people's minds and turning them into said homicidal time-bombs in (yet again) Relative Difficulties.
Another rule that has been really finalised this time round is the exclusion of Devotees. This can allow players to force a parentage on their character ("Look! I have a Chaos Devotee, so I CAN get shapeshift and Logrus, so there!") despite the rarity of true dual-bloods. This ties in with the fact that the GM has ALWAYS decided the parentage of characters as they have almost always been raised by family (or 'family') in Shadow (Andreas being the only real exception). Thus this aspect of the Devotee is always a hindrance to the GM's 'evil plans'.
Since the primary use of the Devotee is this parentage-lever effect, the other use of a Devotee (the support part) is taken up by the Ally and Friend 'advantages' instead.
A small part of the Stuff system that was in use for much of the Relative Difficulties game was the concept of Aura. By spending a single point on a 'Good Aura' people would look upon your character more favourably; you would be more of a 'people person'. By having a 'Bad Aura' you would get a point back, and appear darker and colder than everyone else, grim and unfriendly.
While a good idea in systems with "reaction rolls", such ideas were finally put aside in favour of good old-fashioned role-playing.
Magic, and Sorcery in particular, got heavily over-used in Relative Difficulties. Spell maintenance times were around a tenth of the casting time per week; most combat spells could be reset in three to six minutes! Those with [POWER] Sorcery generally had their maintenance times reduced, if not eliminated entirely. This, along with the infamous "Searchlight of Power Effect", made Sorcery THE power to possess. People used it for combat (disregarding weapons almost completely) and for transportation (Trump went into second place!). Even the famous twenty four hour NightGuard summoning spell (Named and Numbered armoured, Deadly Damage, super Warfare soldiers) took only two and a half hours to maintain a week!
So two major changes were made. Firstly, no spell can act across Shadow; how does one take into account the "Magic of Shadow" of all the Shadows between origin and destination? Secondly, spells take longer to maintain, judged roughly based on the example given in the gamebook (for a change!) : "the average sorcerer has about a dozen spells racked, requiring twenty hours a week of maintenance" (roughly paraphrased).
In Relative Difficulties Basic Pattern was just a travel tool, and in many ways supplanted by sorcerous teleportation. Now it is back to full power, backed up with information from the books and the gamebook. Probability Manipulation (or whatever you choose to call it) is back with a vengeance, as is the ability of Minor Shadow Manipulation.
In Nine Princes, Random changes his and Corwin's clothing completely and without Corwin noticing. If that is possible, almost anything is (within reason, of course). Making oneself clothed appropriately for a Shadow is easy; money can literally appear in a wallet that needed to be there irrespective of probability. While this may seem powerful, it takes time (more depending on the size of the 'change') and can confuse the locals. Clothing can be done as one enters a Shadow; no one need ever know about one's slowly filling wallet or purse.
Powerful? How else do you justify such a massive fifty point expenditure?
Some modifications to the "combat system" is inevitable, simply because it is so vague.
One is the removal of the Attribute Auction (how can you have a secretive game where everyone knows who can beat who?) and the Rank system; attributes are directly compared numerically instead (how? ask the GM).
Another is the Strength option with Warfare, copied (at least in part) from somewhere (there are so many sites; if you recognise this, contact me). Half of a character's Strength attribute can be added to Warfare in melee combat; this takes into account that character's usage of strength-related moves and techniques, and thus allows a very strong individual to simply beat a moderately superior opponent into the ground and smash through his defences.
Somehow Endurance is figured in, but I'm not sure how yet; no fight has come down to Endurance yet, so I guess we will find out when one does.