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The trainer system manages all NPC trainers, their Pokémon teams, AI strategies, and prize money calculations.

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Trainer Classes

All trainer classes are defined in constants/trainer_constants.asm: 
const_def
trainer_const NOBODY         ; $00
trainer_const YOUNGSTER      ; $01
trainer_const BUG_CATCHER    ; $02
trainer_const LASS           ; $03
trainer_const SAILOR         ; $04
trainer_const JR_TRAINER_M   ; $05
trainer_const JR_TRAINER_F   ; $06
trainer_const POKEMANIAC     ; $07
trainer_const SUPER_NERD     ; $08
trainer_const HIKER          ; $09
trainer_const BIKER          ; $0A
There are 48 trainer classes (NUM_TRAINERS = 47, excluding NOBODY). The trainer_const macro automatically generates both the class ID and an opponent ID offset of 200.

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Trainer Constant Macro

The macro creates two constants per trainer: 
MACRO trainer_const
    const \1
    DEF OPP_\1 EQU OPP_ID_OFFSET + \1
ENDM

DEF OPP_ID_OFFSET EQU 200
Example: YOUNGSTER becomes:
  • YOUNGSTER = $01 (trainer class)
  • OPP_YOUNGSTER = 201 (opponent ID for battle system)

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Trainer Data Structure

Trainer parties are defined in data/trainers/parties.asm with two formats:

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Format 1: Same Level

All Pokémon at the same level: 
; if first byte != $FF, then
;   first byte is level (of all pokemon on this team)
;   all the next bytes are pokemon species
;   null-terminated

YoungsterData:
; Route 3
    db 11, RATTATA, EKANS, 0
    db 14, SPEAROW, 0
; Mt. Moon 1F
    db 10, RATTATA, RATTATA, ZUBAT, 0
; Route 24
    db 14, RATTATA, EKANS, ZUBAT, 0

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Format 2: Custom Levels

Each Pokémon has individual level: 
; if first byte == $FF, then
;   first byte is $FF (obviously)
;   every next two bytes are a level and species
;   null-terminated

BrockData:
    db $FF, 12, GEODUDE, 14, ONIX, 0
Format 2 (starting with $FF) is typically used for Gym Leaders, Elite Four, and your Rival, where Pokémon have carefully balanced levels.

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Trainer Data Pointers

Each trainer class has a pointer to its party data: 
TrainerDataPointers:
    table_width 2
    dw YoungsterData
    dw BugCatcherData
    dw LassData
    dw SailorData
    dw JrTrainerMData
    dw JrTrainerFData
    dw PokemaniacData
    dw SuperNerdData
    dw HikerData
    ; ... more classes ...
    dw LanceData
    assert_table_length NUM_TRAINERS
1

Class ID Lookup

Game uses trainer class ID to index into TrainerDataPointers.
2

Party Selection

Within each class’s data, the game selects the specific trainer by index (e.g., “Youngster #3”).
3

Party Loading

Parses the party data format and loads Pokémon into battle.

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Trainer Names

Trainer names are stored in data/trainers/names.asm as null-terminated strings. Each class gets:
  • A class name (“YOUNGSTER”, “LASS”, etc.)
  • Optional individual names for important trainers
Most regular trainers share a class name. Only significant trainers (Gym Leaders, Elite Four, Rival) have unique names.

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Prize Money

Prize money calculation uses base values from data/trainers/pic_pointers_money.asm: 
TrainerPicAndMoneyPointers:
    ; Format: trainer pic, base money
    dw YoungsterPic,    $0F  ; YOUNGSTER
    dw BugCatcherPic,   $0A  ; BUG_CATCHER
    dw LassPic,         $0F  ; LASS
    ; ... more trainers ...
Prize money formula: 
Prize Money = Base Value × Highest Pokémon Level
Elite Four members and Gym Leaders have higher base values, resulting in larger payouts even though the formula is the same.

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Trainer AI System

AI behavior is controlled by engine/battle/trainer_ai.asm with class-specific modifications.

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AI Pointers

TrainerAIPointers:
    dw AI_Youngster    ; YOUNGSTER
    dw AI_BugCatcher   ; BUG_CATCHER
    dw AI_Lass         ; LASS
    ; ... more classes ...
Each AI routine can:
  • Evaluate type matchups
  • Prefer status moves in certain situations
  • Switch Pokémon strategically
  • Use healing items (some trainers only)

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Move Choice Modifications

From data/trainers/move_choices.asm: 
TrainerClassMoveChoiceModifications:
    ; Bit flags for AI behavior
    db 0             ; YOUNGSTER (no special AI)
    db 1 | 2         ; BUG_CATCHER (prefers super effective)
    db 0             ; LASS
    db 1 | 2 | 4     ; SAILOR (advanced AI)
  • Bit 0 (1): Prefer moves that are super effective
  • Bit 1 (2): Avoid moves that are not very effective
  • Bit 2 (4): Prefer status moves when appropriate
  • Bit 3 (8): Prefer moves with high power
Not all trainer classes have sophisticated AI. Early-game trainers (Youngster, Lass) have minimal AI, while late-game trainers use multiple AI flags.

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Trainer DVs

From constants/battle_constants.asm, trainer Pokémon use fixed DVs: 
DEF ATKDEFDV_TRAINER EQU $98
DEF SPDSPCDV_TRAINER EQU $88
These values translate to:
  • Attack DV: 9
  • Defense DV: 8
  • Speed DV: 8
  • Special DV: 8
  • HP DV: 8 (calculated from other DVs)
Trainer Pokémon have slightly above-average DVs (8-9 out of 15), making them stronger than typical wild Pokémon but not perfect.

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Rival Battles

The Rival is special, with three separate class IDs for different points in the game: 
trainer_const RIVAL1         ; $19 - Early game
trainer_const RIVAL2         ; $2A - Mid game
trainer_const RIVAL3         ; $2B - Late game & Champion
Each class has different party configurations depending on:
  • Which starter the player chose
  • Current point in the story
  • Location of the battle

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Rival Party Structure

The Rival’s team adapts based on the player’s starter:
  • If player chose Bulbasaur, Rival has Charmander
  • If player chose Charmander, Rival has Squirtle
  • If player chose Squirtle, Rival has Bulbasaur

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Special Trainers

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Professor Oak

trainer_const PROF_OAK       ; $1A
Has party data defined but is never fought in normal gameplay. His team exists in the code for debug/testing purposes.

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Giovanni

trainer_const GIOVANNI       ; $1D
Battled multiple times with progressively stronger teams:
  • Team Rocket Hideout
  • Silph Co.
  • Viridian Gym (final battle)

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Team Rocket Grunts

trainer_const ROCKET         ; $1E
The most common enemy class, with numerous generic grunts throughout the game.

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Trainer Encounter Flags

Each trainer has a unique event flag that tracks whether they’ve been defeated. This prevents re-battling and is used to give rewards. When a trainer is defeated:
  1. Their event flag is set
  2. Prize money is awarded
  3. Their dialogue changes to post-battle text
  4. They no longer trigger battles when approached

Battle Engine

How trainer battles work

Pokémon

Trainer Pokémon stats

Reference

Trainer constants

Data Structures

Trainer party formats

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Key Files

  • constants/trainer_constants.asm - Trainer class IDs
  • data/trainers/parties.asm - All trainer party data
  • data/trainers/names.asm - Trainer class names
  • data/trainers/pic_pointers_money.asm - Sprites and prize money
  • data/trainers/ai_pointers.asm - AI routine pointers
  • data/trainers/move_choices.asm - AI behavior flags
  • engine/battle/trainer_ai.asm - AI implementation

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