I came up with some ideas to make one or two heroes games playable and fairly balanced, without doing too much work in modifying the game. I post them here, not in "Descent home-brews", because they are just rough ideas, not a polished and tested systems, and I just wanted to hear if other Descent players thought they could work or if there is some crucial error in my reasoning.

I know that I can still play four players game, anyway I just wanted to have fun in finding some way to make one or two heroes game reasonable. Also, with just two heroes, book keeping and equipment management take away less time, and multiclass become more useful, so this kind of game could appeal to someone.

These rules are based on two key concepts:
1. Four heroes games are more or less balanced (I think the majority of Descent players think this).
2. Insted of making the monsters weaker, make the heroes stronger.

The following rules apply to two heroes game. It is still possible to apply them to solo games with some simple scaling. They are instead difficult to apply to three player games (which, anyway, are already reasonably balanced the way it is).

Wounds, fatigue and conquest points
Heroes get double wounds and fatigue. When they are killed the party loses double conquest points.
Healing potions work normally, vitality potions allow to only recover half of the total fatigue.
Example: Mordrog starts with 32 wounds and 6 fatigue. When he is killed the party loses 8 CPs.
Notes: the increased wounds allow the reduced party to sustain the same amount of punishment of a full party. The extra fatigue allows to trigger skills more often, and it comes in handy with the modified action rules explained later. Extra CPs are a way to balance everything, since killing a hero in a two players games is like killing two heroes in a four players game.

Actions
Each hero gets two actions when activated. The first action is declared and resolved, than the second action is declared and resolved, than the other hero's turn begins.
Skills and abilities that are triggered when a specific action is taken work normally, and can be activated multiple times in a turn. Example: Mordrog has the knight skill. If he takes two battle action he can trigger it two times, one time at the end of each action, by spending one FP each time.
A hero is limited to two movement half action per activation, regardless of the number of actions. So a hero cannot run two times, or run and advance, but still he can run and battle, or advance two times.
MPs that are unused during the first action are taken over to the second action (that is to say, when the hero takes a movement half-action he gets MPs for the entire activation, not just for the current action), while attacks that are not used are wasted. Orders may be placed at any moment, even at the end of the heroes turn (so, for example, a hero could take an order action and then a run action, and place an aim order after the movement).
A hero may place multple orders. He may also have multiple orders of the same type, with the exception of dodge orders. Rest orders allow to recover only half fatigue (for example, Mordrog would only recover 3 fatigue, even if his total fatigue is 6). When the hero is wounded and has multiple orders that are removed by wounds, only one of this is removed, chosen by the Overlord. All others conditions removes all susceptible orders.
A hero may drink two potions in a turn.
Notes: these rules allow the reduced party to have the same attack rate and the same "guard capacity" of a full party. The movement limit is necessary to prevent the heroes from sprinting through the dungeon in a few turns.

Line of sight
Each hero as a special "familiar", which works just like Boggs the Rat.
Notes: this rules allows the reduced party to have roughly the same LoS covering of a full party.

All other rules remain the same. So, no extra money, treasures or skills, for example. I was wondering if any has some idea, and thinks this system is broken some way. I didn't think too much about it so it is perfectly possible. I'm especially doubtfult about the actions part.

I tried something much more simple, only 2 things:

#1: use spawn marker from RtL (15 threat or reveal new area to activate it again)

#2: potions heal 5 wounds

guess what? They work like a charm! Makes shorter games too (less monsters, less drag)

Some things I notice:

Health: Giving each hero a larger pool of health will tend to make healing more effective, even with their conquest doubled, because they're less likely to waste it with overhealing, or to die too quickly to get an opportunity to heal. It also means that there's a larger buffer before the first conquest loss, which will sometimes mean the overlord needs one more "kill" before he wins than otherwise.

Actions: Even with the limit of 2x speed per turn, any time the heroes would have moved in a group, your rules don't require the small group to spend as many actions on movement as a large group would, which leaves more actions left over for attacking, resting, etc. For example, if a group of 4 heroes would all advance into a room and each make one attack, your group of 2 can Advance-Battle, getting into the same position but making 6 attacks to the other group's 4.

Also, if a large party puts up 2 dodge orders, the monsters have the option of focusing on the other two characters. Your small group can put up dodge orders on everyone for a smaller action cost, again leaving more actions for attacks, guarding, etc.

You haven't said anything about potions. It would be consistent with your overall strategy to allow heroes to drink 2 potions per turn (maybe specifically limited to 1 per action), though heroes would need to be able to purchase and carry twice as many potions in order to take advantage of that. Then again, maybe you're deliberately screwing the small party on potions in order to try to balance out the other stuff? I'm rather skeptical about how that would work.

You also need a rule clarifying how effect tokens work with the two-actions-per-turn rule. Do you roll for Burn/Daze/Frost/Web multiple times? If you only roll once, the tokens affect more of your actions than for a large party. If you roll twice at the turn start, they affect fewer of your actions. Even if the second roll isn't until after your first action, you can rearrange your action order to minimize their effects, especially since movement points and orders carry over into the second action. Also, what happens if you're stunned?

Line of Sight: LOS coverage against spawning isn't as simple as how many squares you're blocking; it's more a matter of how close the monsters can spawn to your heroes. If one of your heroes needs to stand near a blind corner in order to cover the rest of the room, you haven't really gained anything, because monsters can spawn around the blind corner and attack him, when that would've been too far if the hero simply stayed with the party. Your familiars allow the heroes to cover a bigger area without creating more points where the monsters can attack them, which means your small party will probably be significantly safer from spawns than a 4-hero party (even ignoring the extra dodge/guard orders your party has). Plus, the familiars don't use up the hero's movement in order to get into out-of-the-way positions, so the small party gains another action advantage.

As I've mentioned in a couple other threads, I'm currently finishing up a massive rebalance of Descent, entitled The Enduring Evil , which, among other things, addresses scaling issues--it includes stats for 2-5 heroes. But it's not compatible with standard quests or cards--mostly because monsters are individually much harder to kill.

Thank you, your help is much appreciated. I will take some time to think about this.

Anyway, I'm really curious about your rebalancing project. When will it come out, approximately? And can it be used without expansions?

It's designed to take advantage of the (non-campaign) expansions (WoD, AoD, and ToI), but you should be able to play at least the first quest with only the base game, and some others with just the base game plus Well of Darkness. I also plan to write up some quick hacks you can use to play further without all the expansions if you want, like monster substitutions and such, though they naturally won't work as well as actually having all the stuff.

I'm hoping it will all be ready in a couple weeks now. The bottleneck may be in getting ToI map icons for some of the quests; I wrote FFG to see if they could supply them (since they clearly support fan-made quests), and I got an immediate note saying my request had been forwarded to the correct person, but no further replies yet. I may just have to scan them.

Well, as long as I can personally design scenarios without expansions, I think I could still find it really interesting.

Anyway, what about this:

1. Wounds and fatigue do not change. Each hero gets a "life". When he dies he may spend his life to stay where he is, instead of going to town, but all other death effects are normally applied. When he is killed and goes to town he gets his life back if he has already spent it. Monsters can concentrate attacks to just two heroes, and this is a disadvantage to the party. To balance this each hero is worth one CP less (or the party gets more CPs, don't know). Perhaps, it could be kept the reduction of CPs, even without using lives.

2. Heroes get a single action as usual, but the number of attacks is doubled (so, four for battling, two for advancing, etc). Skills that give extra attacks also give double the normal amount. As part of a ready action, a hero may take two aim or guard orders, but only one rest or dodge order. Movement is unchanged.

3. Lingering effects work normally Poison shouldn't be a problem, fire should also work. Perhaps web, stun and monkey transformation might result being more harmful for the party.

4. Line of sight: perhaps it is better to leave line of sight as it is, and simply increase the threat cost for spawning (by 1 or 2 points).

Do you think it would work reasonably? Of course it isn't perfect, and I don't really know if it can be without major changes in the rules, but as long as it could work without major exploits I can be satisfied with it.

In my experience, monsters concentrate their attacks no matter how many heroes exist. But even if you assume the heroes can somehow force the monsters to distribute their attacks in a manner that is optimal for the heroes, that gives the larger party a fixed conquest bonus (they get to "ignore" damage equal to slightly less than it would take to kill the two "extra" heroes), not a bonus proportional to the number of deaths, so giving the smaller party more starting conquest would seem to make more sense than reducing their conquest values. Even then, the difference is no bigger than what you could get with a party of all high-conquest heroes versus a party of all low-conquest heroes (depending on the exact conquest total), so it's probably in the noise.

Giving out two aim orders is kind of silly, but no more silly than giving out one aim order, I guess. You could frankly give out infinity aim orders for the cost of one half-action (equivalent to saying "aim orders don't get used up when you use them to make aimed attacks") and I don't think you'd upset the game's balance in the slightest (considering you still lose them all if you move, change equipment, or suffer wounds).

Spawning is fairly broken, if for no reason other than that most spawn cards are fairly broken, but short of a rewrite, that seems fairly reasonable.

Regarding Enduring Evil , I see no problem with designing your own scenarios to play without expansions. Though you won't be able to use all of the cards, of course.