FISSION Critter Modding Mini-Guide

Add a Custom Critter (NPC, Creature, or Enemy)

This guide assumes you have a working mod folder (e.g., mods/mod_mytown.dat/ from the Quick Start Guide). You’ll add a new NPC that can be placed on maps, fight, talk, or follow the player.

1. What You Need

Your existing mod folder: mods/mod_mytown.dat/ (a folder for development, compress into actual .dat for release)

You will create two new files for your critter:

• proto/critters/critters_mytown.lst – lists your custom critter file(s)
• text/english/game/pro_crit_mytown.msg – provides name and description

Plus the actual .pro file – you can export it from the Mapper or copy and modify an existing one.

2. Create the Proto Definition File

File: mods/mod_mytown/proto/critters/critters_mytown.lst

myguard.pro

Each line is the name of a .pro file (without path). You can add multiple lines for several critters.

Optional Overrides

After the filename, you can add key=value pairs to override certain fields:

myguard.pro fid=450 ai=3 script=12

Important: male_fid and female_fid only apply to armor items (ITEM_TYPE_ARMOR). If you are adding a custom armor, these overrides control how it looks when equipped on male/female critters. The values are raw art indices (e.g., from art\critters\), not full FIDs – the engine builds the correct FID automatically.

Why overrides? They let you reuse a base .pro file (e.g., a “human guard” template) but give it a unique look, AI, or behavior using mod assets. Currently the mapper.exe will not support assets in beyond the vanilla games base.

3. Create the Message File

File: mods/mod_mytown/text/english/game/pro_crit_mytown.msg

Each critter gets two consecutive entries: name then description.

{0}{}{Town Guard}
{1}{}{A well-armed protector of the settlement.}
{2}{}{Bandit Leader}
{3}{}{The ruthless boss of a raider gang.}

• The first critter (myguard.pro) will use offsets 0 (name) and 1 (description).
• The second critter (second line in .lst) would use offsets 2 and 3, etc.

Note: The base ID for these messages is generated automatically from your mod name (mytown) and the type (crit). You don’t need to calculate anything.

4. Where to Put the .pro File

The .pro file must be placed in the same folder as the .lst file:

mods/mod_mytown/
        └─  proto/
            └─  critters/
                    ├─ critters_mytown.lst
                    └─  myguard.pro

How to get a .pro file:

• Option A: Use the Mapper - open the Proto Editor, create a new critter, save it as myguard.pro in the mod’s proto/critters/ folder.
• Option B: Copy an existing vanilla .pro (e.g., from proto/critters/) into your mod folder and rename it. The PID inside the .pro file is ignored – FISSION generates its own stable PID from the mod name and filename.

5. Test Your Critter

1. Run the game once (or reload if already running).
2. Check data/lists/proto_list.txt – your critter should appear under “CRITTER MOD PROTOS”.
3. Find the generated PID (e.g., 33686018). You can now use it in scripts:

variable npc_pid;
npc_pid := 33686018;   // use the number from proto_list.txt
create_object(npc_pid, tile, elevation);

6. Important Notes

• PID generation is stable – the same mod name + proto name always produce the same PID. You can safely hardcode the PID from proto_list.txt in your scripts.

• PID Ignored The PID inside the .pro file is ignored – do not worry about what number it shows.

• Hash collisions – if two different mods accidentally generate the same PID, a warning message box appears and the second critter is skipped. Rename your mod or proto to resolve.

• Message IDs – each critter uses two consecutive IDs (name, description). The base ID is allocated per mod, so you never need to assign numbers manually.

• AI packets – Standard AI packets are defined in ai.txt (vanilla: 0 = none, 1 = coward, 2 = aggressive, etc.). You can also add custom AI packets via ai_mytown.txt.

7. Quick Troubleshooting

8. Dialog Heads and Backgrounds (FISSION-specific)

You can give any NPC a talking head and a custom background without editing the NPC’s script. This is useful for adding heads to existing characters, companions, or flavor NPCs.

What You Need

• Head art files (.frm) in art/heads/
• A heads_<mod>.lst file in art/heads/
• (Optional) Background art files (.frm) in art/backgrnd/
• (Optional) Global variables defined via gvar_<mod>.txt for dynamic backgrounds

8.1 Head File Naming (Vanilla Convention)

The engine uses the base name of your head and appends two-letter codes to build the actual filenames.

Note: Vanilla Fallout 2 uses these suffixes (for example, myronnp.frm). The engine does not support custom remapping for dialog heads.

8.2 Create heads_<mod>.lst

Place this file in art/heads/.

Syntax

<basename>,<good_count>,<neutral_count>,<bad_count> npc_script=<script_name> [bg_gvar=<gvar_index>] [background=<bg_index>]

• basename — Base name of the head (for example, myhead).
• good_count, neutral_count, bad_count — Number of fidget frames for each expression (usually 3).
• npc_script — Required. Script basename without .int.
• bg_gvar — (Optional) Global variable index for a dynamic background.
• background — (Optional) Static background index used as a fallback.

Example

myhead,3,3,3 npc_script=FCMer bg_gvar=6991 background=5

This assigns the head myhead to any NPC using the script FCMer. If global variable 6991 contains a value other than -1, that value becomes the background index. Otherwise, background 5 is used.

If both bg_gvar and background are omitted, the NPC uses its normal dialog background.

8.3 Finding Script Names

FISSION generates a list of every loaded script:

data/lists/scripts_list.txt

Use the script’s base name (without .int) as the value for npc_script=.

8.4 Finding Global Variable Indices

If you define globals in gvar_<mod>.txt, FISSION assigns them stable numeric indices. You can find them in:

data/lists/gvars_list.txt

Use the numeric index in bg_gvar=.

8.5 Background Indices

Backgrounds are FRM files listed in backgrnd.lst (or backgrnd_<mod>.lst).

• Place custom background FRMs in art/backgrnd/.
• List them in backgrnd_<mod>.lst.
• The background index is its position in the list, starting from 0.

8.6 Precedence (Important)

FISSION applies dialog heads and backgrounds in this order:

1. Head assignment — If an NPC matches a npc_script= entry, that head is used.
2. Dynamic background — bg_gvar overrides the static background whenever its value is not -1.
3. Static background — Used only when no dynamic background is available.

8.7 Example Workflow

1. Create your head art files (myheadnp.frm, myheadgvf1.frm, etc.) in art/heads/.
2. Create art/heads/heads_mymod.lst:

myhead,3,3,3 npc_script=FCMer background=2

1. (Optional) Define a GVAR in gvar_mymod.txt:

MY_BG = -1

1. Find its assigned index (for example, 6991) in gvars_list.txt and update the entry:

myhead,3,3,3 npc_script=FCMer bg_gvar=6991 background=2

1. Change the background from any script:

set_global_var(6991, 5);   // Background index 5

The next time the player talks to that NPC, background 5 will be displayed automatically.

8.8 Notes

• Works with any NPC, including companions, merchants, and quest givers.
• The NPC’s script does not need to call set_head() or set_background().
• Multiple NPCs can share the same head by adding multiple npc_script= entries.
• Head assignment is based on script name, not PID, making it more reliable when different NPCs share the same prototype.

9. What’s Next?

Once your custom NPC is working, give it a unique combat personality with the AI Mini-Guide. You can define aggression, weapon preferences, taunts, and even disposition variants (coward, defensive, aggressive, berserk) that respond to the ai_set_disposition script command.