Until recently, the algorithms and equations used in Mother have been shrouded in scary machine code and undocumented assembly code dumps. But luckily, a few awesome people have showed up to save the day and provide us with some very cool and interesting info. The following are how the game makes its decisions and/or makes its various calculations.
News:
MOTHER / EARTHBOUND ZERO Equations:
Level Experience:
The total experience needed to reach level n = n * n * (n+1) * constant, rounded down.
"constant" depends on person:
| Character | Constant | Approximate Decimal |
| Ninten | 214/256 | 0.84 |
| Ana | 203/256 | 0.79 |
| Lloyd | 3/4 | 0.75 |
| Teddy | 150/256 | 0.59 |
| Pippi | 150/256 | 0.59 |
Teddy starts at level 18 with 3600 experience points. Everyone else starts at level 1 with 0 experience points.
Stat Growth Formulas:
Formula for stat increase during a levelup:
stat gain = (constant + (random number 0-3))/2, rounded down
Constant values:
| Character | Fight | Speed | Wisdom | Strength | Force |
| Ninten | 4 | 4 | 4 | 4 | 4 |
| Ana | 0 | 2 | 6 | 2 | 7 |
| Lloyd | 3 | 1 | 7 | 3 | 2 |
| Teddy | 8 | 8 | 1 | 5 | 3 |
| Pippi | 8 | 8 | 1 | 5 | 3 |
| EVE | 5 | 3 | 5 | 7 | 1 |
| FlynMan | 6 | 0 | 0 | 8 | 5 |
- Increases are regardless of current stat value. Luck can lead to a large variance at higher levels.
- All stats are capped at 255 and will not overflow.
When a levelup is earned, Offense will always increase by an amount equal to the Fight increase. Similarly, Defense will increase an amount equal to the Speed increase.
Increasing your Fight or Speed in other ways will not increase Offense or Defense.
Increases to HP and PP are determined after other stat increases:
HP/PP gain = random number between 0 and N-1, where N = 2*(target value - current value)
- regardless of formula, N has a min value of 2, and a max value of 16
HP: Target value = 2*Strength+20 or Strength+255, whichever is smaller.
PP: Target value = Force*1.5
If your level is high enough to learn a particular PSI power, you have a 1/4 chance of learning it after any battle you win or escape from.
Item Information:
The drop rate from enemies is 1/16 for all items.
Infinitely usable items: Super Spray, Flashdark, Bullhorn, AsthmaSpray, WordsO'Love, Swear Words
Breakable items: Fl Thrower, Laser Beam, Plasma Beam, Insecticide, StkyMachine, PSI Stone
- The probability of an item breaking is always 1/8.
Rope: always hits - the enemy has a 1/4 chance of breaking free each turn.
Bullhorn - always has exactly 50% success-rate.
StkyMachine - inflicts paralysis (like PSI Paralysis)
Battle Formulas:
Physical attacks (using "FIGHT" option):
Dodge rate: [26 + (target's Fight - attacker's Fight)/2]/256
Smash rate: [26 + (attacker's Fight - target's Fight)/2]/256
Damage done is approximately equal to Attacker's Offense - (Defender's Defense / 2).
However, if attacker's offense < defender's defense, then damage is ((Attacker's Offense * 3) - Defender's Defense) / 4
- Damage with SMAAAASH hits ignores the target's defense.
Status Ailment Accuracy:
Probability of evading status ailments: [(defender's Strength or Force)/2]/Attacker's Wisdom
- Strength is used to avoid Darkness, Poison and Paralysis.
- Force is used to avoid Puzzled, Confused and Hypnosis.
- StoneOrigin ALWAYS causes Stone if it hits a non-immune target (it can miss, though).
- Ninten will ALWAYS have an asthma attack when hit by a car exhaust. While affected, the only action he can take is to use an Asthma Spray.
- The same formula is used for status ailments inflicted via PSI, items, or enemy special attacks.
The higher a character's Speed is, the better chance it has of going first.
The chance of running is 50/50. Each character may make an attempt to run once per turn, and on a success, the whole party flees. PSI 4th-D Slip works 100% of the time.
Random Encounters:
Whenever you take a step in an area with random encounters, the RNG generates a number, and you get into a battle if the number is below a certain amount. Here is the list of random encounter probabilities:
1: 32/256
2: 21/256
3: 16/256
4: 13/256
5: 10/256
6: 8/256
7: 6/256
8: 5/256
To decide which one to use, the game takes the number associated with the tile you stepped on (between 1 and 8), adds a "bonus", and uses the probability attached to that number.
The bonus resets to 0 everytime you enter a no-encounter area, and increases by 1 each time you get into a fight. The bonus can't go higher than 2, and it can't increase the category number higher than 8.
Example: You leave a safe town to enter a field full of tiles marked with "2".
- With every step you take, you've got a 21/256 (or about 8.2%) chance of getting into a fight.
- Once you get into your first fight, the odds of getting into your second fight for that area are 16/256 (6.25%) for each step.
- After that second fight, your odds for getting into a fight remain at 13/256 (about 5.1%) for each step for the remainder of your exploration of the area. The "bonus" resets when you go back to the safe town.
