1 - 2 - 3 is a D6 system - no other dice are required!
A Hero has 3 attributes:
Physical, Mental, Social
Distribute 6 points among the attributes so each attribute has a stat from 1-3.
On top of that, Heroes start with 10 skill points to distribute among skills. Skill descriptions can be as broad as "melee combat" or as narrow as "heart surgery in zero gravity" - this depends on player's choice and GM's agreement. A skill's maximum stat is 3!
There are active and passive skills. Active skills require a skill roll to work, passive skills are "always on". Skill rolls work with a number of successes rolled and the number of successes rolled determine the grade of success achieved. For passive skills the player has to work out in cooperation with the GM, how the skill works. As skills depend on attributes, the attribute linked to a skill is a good measure, how strong a passive skill's effect on a Hero is.
When performing a skill roll, roll a number of dice equal to the linked attribute's stat. Each die's result is compared against a difficulty number: 4,5,6 for easy tasks, 5,6, for average tasks, 6 for hard tasks. You receive a number of rerolls equal to your skill's stat to reroll dice that did not end up as a success.
Tools supporting the task at hand give you a +1 per die for a task.
Performing supernatural skills (Magic Spells, Prayers, Psi effects) always is hard! However, you may aquire a "focus" skill, which is an active skill that, too, is always hard, but gives you a +1 per success on each die rolled for the supernatural skill!
Opponents come in 3 levels: Goon (lvl1), Average (lvl2), Boss (lvl3)
They use their level as a stat for everything: attribute stat, skill stat, number of actions, armour stat. (Yes, Bosses are pretty nasty and should be used rarely only!)
The opponent's level also indicates, how many hits they can take:
Lvl1 are out of action permanently after the 1st hit.
Lvl2 are out of action for the moment, but may recover just like Heroes (see below). On the 2nd hit they are out permanently.
Lvl3 shrug off the 1st hit each turn without any consequences. The next hit on a turn, however, takes them out of action for the moment. They may recover just like Heroes (see below). On the 3rd hit (or on the 2nd, if they already are out of action) in a turn they are out permanently.
Combat is extremely deadly: every Hero can only take 2 hits! Take one hit and you are out of action with a chance to recover, take 2 (or more) hits and you are out of action for the remainder of the adventure at the very least!
The armour is a measurement, how easy it is to hit a Hero / an opponent: Armour has got two stats: The first one, called Armour Value, tells you, how easy/hard it is to hurt you, the second, called Action Allowance, tells you the number of actions you have got per turn. (An action can be: move 4", attack once, use a device, use a skill, unlock a door, and so on ..) There is light armour (AV1/AA3), medium armour (AV2/AA2) and heavy armour (AV3/AA1).
In combat each participant PICKS his initiative on a D6 (!) in secret. The GM may opt to roll for Goons and Average opponents but should go for picking the initiative for a Boss!
When everybody has set his initiative, reveal! Order of acting goes from lowest initiative to highest!
As opposed to skill rolls, you don't get an automatic +1 for using a "tool" (rather: a weapon). Instead you get to add your picked initiative to each die rolled. Pick a low initiative to attack first with a chance to miss, pick a high initiative for a better chance to hit but with a chance to get hit first (and thus being taken out of action before you can hit), too. On each die rolled a final result of 6+Target's Armour Value or more is a hit!
Combat equipment in your hands can be:
2 handed melee weapon (giving a +1 on each die rolled)
1 handed melee weapon
1 handed ranged weapon (range: 8", reload on 6+)
2 handed ranged weapon (range: 16", reload on 5+)
Shield (only in combination with a 1 handed weapon; adds +1 to Armor Value for attacks from the Hero's front arc while keeping the Action Allowance)
When attacking with ranged weapons, roll a separate "Reload" die along to the attack to see, whether the weapon needs to reload. Reload a 1 handed weapon for 1 action and a 2 handed weapon for 2 actions. A weapon (or any other piece of equipment you've got) can have a special ability to do more than just damage one enemy. (A flamer, for example, might affect all enemies witin a circle of 2", an acid grenade may attack it's target turn after turn accumulating an additional +1 on each die per turn, and whatever the GM deems appropriate.) In that case add +1 to the dieroll when checking for reload! Also, the weapon needs +1 action to reload!
Supernatural skills can attack opponents, up to 24" away, too. A supernatural skill always has to "reload" on a 5+, no matter what! Then, however, the Hero needs a whole night (at least 8 hours) of rest to "reload" the skill.
A combatant having taken 1 hit is out of action for the moment but can still recover. Recovering uses up all of his actions. Roll 2 dice: on a 5 or more on any one of the dice the combatant recovers and can act regularly at the beginning of the next turn. If the combatant has not been attacked during the previous turn, he recovers on a 4 or more on one die.
A Hero with a medical / healing skill may use this skill to have the combatant out of action recover. The difficulty for this is average at best, hard, if the combatant out of action or the healer is under attack.
After taking a 2nd hit, you are out and at the very least prolonged and advanced medical care is necessary to get you back up. (Read: you don't get to participate in the current adventure any more!)
You get experience for fulfilling tasks rather than for killing opponents:
You need 100XP to buy the first skill point in a new skill, 200XP to buy the 2nd skill point and 300XP for the 3rd skill point.
Killing a goon gives you 1XP, an average opponent 2XP and a boss 3XP.
Fulfilling main missions gives you 50-100XP (GM's discretion), fulfilling sidequests gives you 10-50XP (GM's discretion). Aiding in fulfilling missions but not surviving until the end gives half XP (but still full XP, if you go down during the final battle!)
