ACKS does not have a core mechanic in the sense that systems such as GURPS, D6, or Marvel Superheroes have a core mechanic, which is to say, one all-purpose die roll + modifiers that handles all actions in the game. What it does have is a series of similar game mechanics that are applied to similar situations. Our philosophy is that "similar situations should be similarly simulated, but different situations should be simulated differently." One very common game mechanic is called a throw. A throw occurs whenever a character or monster is taking an action that will either succeed or fail. For instance, when a character tries to avoid a catastrophic event, his player makes a saving throw. When a character attempts to strike an opponent in combat, his player makes an attack throw. When a character attempts to open a lock, bash down a door, or sneak down a hallway, his player makes a proficiency throw. To make a throw:
- Throw the appropriate die for the action chosen.
- Add any relevant modifiers to the number generated by the die.
- Compare the total to the character's target number for the action, usually expressed as #+ (such as 12+).
If the total equals or exceeds the target number, the outcome is favorable to the character. If the result is lower than the target number, the outcome is unfavorable to the character. The target number required to succeed at different throws is usually based on the character’s class and level. For instance, fighters have easier attack throws than other than characters, while thieves have easier proficiency throws to sneak around. We believe the "throw" mechanic has major benefits, compared to various alternative systems available:
- The throw mechanic directly, rather than indirectly, informs the player of the information he needs to know, i.e. "what number do I need to roll on the die." This number can be listed directly on the character sheet: "Hear noise 14+" "Save v. Death 11+" "Attack with sword 9+".
- The throw mechanic puts the emphasis on the character, rather than the situation. A player understands that if he has "Hear Noise 14+" in most circumstances his character can eavesdrop on a roll of 14-20. If there is a modifier to this chance, it's transparent to the player: "A penalty of -4 to your roll due to the loud noise". In contrast, systems such as 3.5 or 4e, which use a fixed bonus against a variable Difficulty, put the emphasis on the GM's decision as to the situation. Very often the GM is actually encouraged to calculate what chance he wants for success, and to then 'customize' the Difficulty accordingly (this is explicit in 4e). These sort of accounting illusions are unnecessary in ACKS. Where we believed a task should be equally challenging for characters of varying level, we simply either use a type of throw that doesn't change with level (such as the proficiency throw to find secret doors), or we use a roll (see below).
The other major mechanic used in ACKS is the roll. A roll is used when there are a range of possible outcomes. When a character meets a monster during an encounter, the GM will make a reaction roll to see how the monster reacts to the character, with results ranging from friendly to hostile. When a character is in combat, the players will make an initiative roll to determine when he gets to act, with results ranging from last to first. When a character hits an opponent, the player will make a damage roll to determine how many hit points his target loses. When monsters begin to lose a battle, they will make a morale roll to determine if they stay and fight, flee, or surrender. While there are some unique rolls for very special cases, such as teleportation mishaps, most rolls are made with either 1d6 (surprise, initiative, and most damage rolls) or 2d6 (reactions and morale). The 2d6 reaction roll mechanic is used frequently throughout ACKS, with slight variation: Monster reactions; hireling reactions to offers; hireling monster; monster morale; and domain confidence all use the 2d6 reaction roll. Altogether, these two bundles of mechanics -- throws and rolls -- handle 99% of the action in ACKS. We think they are a wonderful compromise between the simplicity of universal mechanics and the fun factor of specialized mechanics.