This has mostly been supplied to me by Rusty, for which I thank him profusely. It has been edited quite a lot in bits due to the differences in our two games, the edits being mainly done by myself and Lord Oddeye. So, huge thanks going out to Rusty and Lord Oddeye!

Max level is 20 prior to first promotion. Earliest level for first promotion is level 10. Later promotions may prove benefitial. Limit after first promotion is 30. Earliest level for second promotion is level 20 promoted.

Actions: (Note: item refers to both items and weapons)
Attacking, staying, casting a spell, giving an item/trading items, and using an item all count as actions. You can only perform one action a turn. Changing equipment on your turn does NOT count as an action. Nor does dropping an item.

You can hold a total of 6 items, one of these slots being for a weapon ONLY and another for an accessory ONLY. Note that Force members cannot attack unarmed.

Stats: HP, MP, Attack, Defence, Agility, Movement, Luck

HP - Hit Points: When HP reaches 0, your character is defeated and must be raised
MP - Magic Points: When MP reaches 0 or below the least costing spell, you can no longer use any spells for the rest of the battle
Attack: Attack affects damage
Defence: Defence affects how much a character takes
(Damage = Attack - Defence)+/- land effect
Agility: Affects evade rates and counter rates
Movement: How far a character can move on a surface
Luck: Affects evade rates, critical rates, status effects, etc. (varies by race and class)

HP, MP, Attack, Defence and Agility can be increased on level ups. Movement and Luck cannot. Stat gains on level ups are going determined by class and luck. Race does not affect any stats other than Movement and/or Luck.

Evade rate = 1/4 Speed (round down always) + Luck [equal or less on d100 = success]
Critical rate = 1/8 Level (round down always) + Luck [equal or less on d100 = success]
If a character makes a critical attack and has gained weapon proficiencies, then a special attack replaces the ordinary critical. These special attacks are generally more powerful than a normal critical and some cause status effects.
On the critical hit roll, roll 1d100 for each special in the character's list

Level 0 weapon mastery = 1d100 (Normal critical hit)
Level 1 weapon mastery = 1d100 (Level 1 special)
Level 2 weapon mastery = 2d100 (Level 1 special + Level 2 special)
Level 3 weapon mastery = 3d100 (Level 1 special + Level 2 special + Level 3 special)
Additional rule : Roll one more d100 if the character's weapon has a special and always consider this special as being of the highest level. (see explanations below)

Read the obtained numbers from left to right and stop on the first one that meets the requirements for a critical hit. Corresponding special will be unleashed, the leftmost number being the special of highest level that a character can use. The first number to meet the requirement for a crit wins.
Critical damage = +50% to Regular Damage for a normal critical and level 1 specials. +55% for level 2 specials and +60% for level 3 specials. The minimum damage a critical hit can deal is 8 if a weapon is equipped. It is 5 if there is no weapon equipped. I don't know why this is, or how it works, but it just seems to be the case. Spells can’t critical hit.

Damage variability (a d100 is rolled for each attack):
1-32 = low (roll 1d15 and reduce damage by x%. round down)
33-65 = medium (normal damage)
66-100 = high (roll 1d15 and increase damage by x%. round down.)
Both attacks and spells are affected in this way. Damage dealt by spells can also be affected by spell resistance.

Status effects = Spell's hit chance + Luck* [equal or less on 1d100 = success]
Counter rate = 1/8 Speed (round down always) + Luck [equal or less on 1d100 = success]
Counter damage has no penalty to it – it’s dealt as if it was a regular attack.

To determine results, such as attacks, effects, etc., a 1d100 is rolled.

First roll: Hit Chance
Second roll: Damage roll (if hit)
Third roll: Critical Rolls (ranges from 1 to 4)(if hit)
Fourth roll: Counter Chance (if no critical)
Fifth roll: Damage roll (if counter)

There are no double attacks in this game. If the attacking character makes a critical, then they cannot be countered. Counter attacks cannot critical. If a counter occurs, it happens simultaneously to the initial attack, so the character being attacked can be killed by the attacker, but still deal counter damage back. A character cannot evade an attack and then counter.

Land Effect:
15% = Damage is treated as 15% lower (minimum 1 damage dealt)
30% = Damage is treated as 30% lower (minimum 1 damage dealt)

Magic Resistance:
Very weak = +1/2% damage from the spell
Weak = +1/4% damage from the spell
Strong = -1/4% damage from the spell
Very strong = -1/2% damage from the spell
Though Magic Resistance at the moment is much generalised, it only applied to normal monsters. Bosses and more important characters will have Magic Resistances like Force members do. A Force member’s magic resistance decreases (or increases if it’s negative) by a percentage equal to the magic resistance. So if a Force member has a Fire magic resistance of 10 and is dealt 10 damage by a Blaze spell, she’d only take 9 damage.

3 = -10% to spell's hit chance, 4 turns affected/40% chance of poisoning or paralysis
4 = -15% to spell's hit chance, 3 turns affected/30% chance of poisoning or paralysis
5 = -30% to spell's hit chance, 3 turns affected/25% chance of poisoning or paralysis
6 = -45% to spell's hit chance, 2 turns affected/20% chance of poisoning or paralysis
7 = -60% to spell's hit chance, 2 turns affected/15% chance of poisoning or paralysis
8 = -75% to spell's hit chance, 1 turn affected/10% chance of poisoning or paralysis
9 = -90% to spell's hit chance, can't be affected

Note: Both the caster and target's Luck apply*. (If the caster's Luck exceeds the target's Luck by two or more, the caster's Luck is treated as one lower, but used, for an increase in possible effect. If the caster's Luck is one higher or the same as the target's Luck, the target's Luck is still used.)

Charmed: The caster/charmer controls the charmed target(s)
Confused: 1-33% = Act as normal, 34-66% = Do nothing, 67-100% = Attack friend
Illusion: Attacks are 50% less accurate.
Paralyzed: Actions are only 20% likely to be successful.
Poisoned: Loses HP each round. Poison has a particular power, depending what creature it comes from. This power number is a percentage. When something is poisoned, you remove x% HP from it each turn the poison is present.
Sleep: Character falls asleep and skips turns while asleep
Curse: Some turns the character will be paralysed and the character also loses HP at random. Chaos Ring nullifies effects
Frozen: Character cannot move. Effects wear off after 1 turn. Whilst frozen, a character's evade rate drops to 0.

Priest Charges:
Cure: 20 for Poison, 1/4 Item/Weapon Price for Curses
Promotion: Free
Revive: 50 gold per character level

Shop Charges:
Sell: 3/4 the listed price
Repair: 1/4 the listed price

Weapon/Accessory Break Chance: 1-30% = Crack, 31-100% = No break (high = good) - Luck applies

A note about weapon/spell ranges

Here's a bit of clarification how a range of 3 works in this game, as there are many people who have not played SF3 and as such will not know how it differs from other SF games. It is easiest to show how the ranges work by displaying a picture. Look here to see it. The red square denotes where the character is attacking/casting from. He/she can target anything within the range of green squares.