Phenotype Variations

Phenotype & Variations

Overview

Each creature in Icarus has a visual phenotype (skin/coat variation) controlled by a single integer field in the save data. The game defines a Variations array per creature type in a dedicated IcarusMount DataTable inside data.pak, containing mesh materials, fur materials, and spawn weightings.

Key finding (extracted from current data.pak dated Feb 27 2026): Only 3 of 28 creature types have color variations via the Variations system. The remaining 25 types have a single fixed appearance.

The `Variation` Field

The Variation property is an IntProperty in each creature's binary data blob. It is a 0-based index into the creature's Variations array in the game's IcarusMount DataTable.

Field	Type	Location	Description
`Variation`	IntProperty	Binary blob	Index into the creature's Variations array
`CosmeticSkinIndex`	IntProperty	IntVariables array	Always `-1` (unused)
`LinearColorVariables`	ArrayProperty	Binary blob	Always empty (unused)
`ChildDNA.UniqueVariation`	IntProperty	ChildDNA struct	Always `0` (unused)

Only Variation controls the visual appearance. The other fields exist in the data but are not actively used by the game.

How It Works

Each creature type has a row in the IcarusMount DataTable (RowStruct: /Script/Icarus.IcarusMount) inside data.pak
Each row may contain a Variations array with entries containing:
MeshMaterial — the creature's body material/texture path
GFurMaterial — the creature's fur/groom material path
CarcassMeshMaterial — the carcass body material (same for all variants)
CarcassGFurMaterial — the carcass fur material (same for all variants)
Weighting — spawn probability (higher = more common)
The Variation integer in the save data selects which entry from this array the game renders
Variation = 0 is always the common/default appearance
Types with no Variations array have only one visual appearance — their Variation field is always 0

Confirmed by Comparison

Comparing same-type creature pairs with different appearances:

Mount Name	Type	Variation	Material	Rarity
Bill	Buffalo	0	MI_CRE_Buffalo	Common
Higgs	Buffalo	4	MI_CRE_Buffalo_Rare_VarH	Rare
Kupo	Moa	0	M_CRE_Moa	Common
Tawhiri	Moa	1	M_CRE_Moa_Var5	Rare

All other differences between pairs were gameplay-related (stats, position, name, level, talents) — not appearance.

Complete Variation Catalog

Source: Extracted from data.pak (Feb 27 2026) at Content/Data/data.pak in the Icarus game installation. The IcarusMount DataTable contains 28 creature type rows. Data was extracted by decompressing all 722 zlib chunks and parsing the JSON-like structure.

Summary

Category	Count	Types
Color variations (Variations array populated)	3	Buffalo, Moa, Wolf
Single appearance (no Variations)	25	All others
Total variants	24	8 per type × 3 types

Rarity Tiers

Rarity is determined by spawn weighting:

Weighting	Rarity	Typical
≥ 1000	Common	Default appearance
100–999	Uncommon	—
25–99	Rare	Named color variants
5–24	Legendary	White, special patterns
< 5	Ultra-Rare	—

Buffalo (8 variations)

Index	MeshMaterial	GFurMaterial	Weight	Rarity
0	MI_CRE_Buffalo	MI_CRE_Buffalo_fur	2000	Common
1	MI_CRE_Buffalo_Rare_VarC	MI_CRE_Buffalo_Rare_VarC_Fur	50	Rare
2	MI_CRE_Buffalo_Rare_VarD	MI_CRE_Buffalo_Rare_VarD_Fur	50	Rare
3	MI_CRE_Buffalo_Rare_VarG	MI_CRE_Buffalo_Rare_VarG_Fur	50	Rare
4	MI_CRE_Buffalo_Rare_VarH	MI_CRE_Buffalo_Rare_VarH_Fur	50	Rare
5	MI_CRE_Buffalo_White	MI_CRE_Buffalo_White_fur	5	Legendary
6	MI_CRE_Buffalo_Legendary_VarA	MI_CRE_Buffalo_Legendary_VarA_Fur	5	Legendary
7	MI_CRE_Buffalo_Legendary_VarB	MI_CRE_Buffalo_Legendary_VarB_Fur	5	Legendary

Moa (8 variations)

Index	MeshMaterial	GFurMaterial	Weight	Rarity
0	M_CRE_Moa_MI	M_CRE_Moa_fur	2000	Common
1	M_CRE_Moa_Var5	M_CRE_Moa_Var5_Fur	50	Rare
2	M_CRE_Moa_Var8	M_CRE_Moa_Var8_Fur	50	Rare
3	M_CRE_Moa_Var9	M_CRE_Moa_Var9_Fur	50	Rare
4	M_CRE_Moa_Var10	M_CRE_Moa_Var10_Fur	25	Rare
5	M_CRE_Moa_Var11	M_CRE_Moa_Var11_Fur	25	Rare
6	M_CRE_Moa_Var12	M_CRE_Moa_Var12_Fur	25	Rare
7	M_CRE_Moa_Var13	M_CRE_Moa_Var13_Fur	5	Legendary

Wolf (8 variations)

Index	MeshMaterial	GFurMaterial	Weight	Rarity
0	M_CRE_Wolf	M_CRE_Wolf_Fur	2000	Common
1	M_CRE_Wolf_Rare_VarA	M_CRE_Wolf_Rare_VarA_Fur	50	Rare
2	M_CRE_Wolf_Rare_VarB	M_CRE_Wolf_Rare_VarB_Fur	50	Rare
3	M_CRE_Wolf_Rare_VarC	M_CRE_Wolf_Rare_VarC_Fur	50	Rare
4	M_CRE_Wolf_Rare_VarD	M_CRE_Wolf_Rare_VarD_Fur	50	Rare
5	M_CRE_Wolf_Rare_VarE	M_CRE_Wolf_Rare_VarE_Fur	50	Rare
6	M_CRE_Wolf_Legendary_VarA	M_CRE_Wolf_Legendary_VarA_Fur	5	Legendary
7	M_CRE_Wolf_Legendary_VarB	M_CRE_Wolf_Legendary_VarB_Fur	5	Legendary

Note: Wolf was not present in the older pak-files extraction (Feb 26). Re-extracting from the current data.pak (Feb 27) revealed Wolf as a third creature type with color variations.

Single-Appearance Types (25 types — no Variations)

These creature types have no populated Variations array. Their Variation field is always 0 and there are no alternate visual appearances available through this mechanism.

Creature Type	Notes
Arctic_moa	Biome variant of Moa (separate type, not a Moa color variation)
Blueback	—
Bull	—
Cat	Appearance is controlled by breed (separate ActorClass: BP_Tame_Cat_C, BP_Tame_Cat_B_C, BP_Tame_Cat_C_C)
Chicken	Colors are separate D_Mounts rows (Chicken, Chicken_A2, Chicken_A3), not Variations
Cow	—
Dog	Appearance is controlled by breed (9 separate ActorClasses: BP_Tame_Dog_A1_C through BP_Tame_Dog_E_C)
DogSmall	Small dog sub-type
Horse	Terrenus Horse (single appearance)
Horse_Standard	Colors are separate D_Mounts rows (A1=Brown, A2=Black, A3=White), not Variations
Mini_Hippo	—
Pig	—
Ram	—
Rooster	—
Sheep	—
Snow_Striker	—
Snow_Wolf	Biome variant of Wolf (separate type, not a Wolf color variation)
Swamp_Bird	—
SwampQuad	—
Tusker	—
Zebra	—
Wild_Boar	—
Wolf_Desert	Biome variant of Wolf (separate type, not a Wolf color variation)
WoollyMammoth	—
WoolyZebra	—

Visual Variation Mechanisms — Complete Reference

The game uses three distinct mechanisms for creature visual differences:

1. Variation Array (Color Variants)

Applies to: Buffalo, Moa, Wolf
Mechanism: Variation IntProperty indexes into IcarusMount Variations array
Editable: Yes — change the integer value (0 to 7)
In save data: Variation field in binary blob

2. Breed / ActorClass (Breed Variants)

Applies to: Dog (9 breeds), Cat (3 breeds), Horse Standard (3 colors), Chicken (3 colors)
Mechanism: Each breed has a separate ActorClass blueprint or separate D_Mounts row name
Editable: Requires changing the creature's D_Mounts row name reference — more complex
In save data: Row name reference in the mount entry

3. Biome / Separate CreatureType

Applies to: Arctic Moa (vs Moa), Snow Wolf (vs Wolf), Desert Wolf (vs Wolf)
Mechanism: Completely separate CreatureType entry
Editable: Would require species swap (see Species & Types)

Phenotype Mutation Talents

Two breeding-tree talents influence the chance of offspring inheriting rare phenotypes:

Talent	Effect per Rank	Max Ranks
Visual Anomaly	+0.05 CosmeticMutationChance	3 (+0.15 total)
Prime Variants	+0.05 CosmeticMutationChance	3 (+0.15 total)

These talents increase the probability that a bred creature receives a non-zero Variation index (i.e., a rarer visual appearance) rather than the common default. They are only relevant for the 3 types that have Variations data (Buffalo, Moa, Wolf).

Binary Format Reference

The Variation field is encoded as a standard IntProperty in the binary blob:

0A 00 00 00                          # name length = 10
56 61 72 69 61 74 69 6F 6E 00       # "Variation\0"
0C 00 00 00                          # type length = 12
49 6E 74 50 72 6F 70 65 72 74 79 00 # "IntProperty\0"
04 00 00 00                          # data size = 4
00 00 00 00                          # array index = 0
00                                   # extra byte
04 00 00 00                          # value = 4 (little-endian)

The value is a signed 32-bit little-endian integer. Valid range is 0 to N-1 where N is the number of entries in the creature type's Variations array (8 for Buffalo, Moa, and Wolf).

Data Source & Extraction

The variation data lives in data.pak at:

<Steam>/steamapps/common/Icarus/Icarus/Content/Data/data.pak

This is a UE4 pak file (~2.1MB) containing 722 zlib-compressed chunks totaling ~35.7M chars of JSON-like DataTable text. The IcarusMount DataTable (RowStruct: /Script/Icarus.IcarusMount) starts in chunk #57 and spans ~91K chars.

Important: The data.pak is updated with each game patch. Our pak-files/ directory contains pre-extracted chunks from an older version (Feb 26). When re-extracting, always use the current data.pak from the Steam installation to ensure accuracy.

Editor Integration

The Appearance dropdown in the Overview Tab allows changing a creature's visual phenotype directly:

Buffalo, Moa, Wolf: Dropdown shows 8 variations, each labeled with index, rarity tier (Common/Rare/Legendary), and material name (e.g., 3: Rare — MI_CRE_Buffalo_Rare_VarG)
All other 25 types: Dropdown shows "Default (single appearance)" and is disabled
Selecting a variation updates the Variation IntProperty in the binary data
On species swap, the variation automatically resets to 0 (common default)
Out-of-range values are prevented by validation in MountModel.variation

Implementation Details

Component	Location	Role
`variation_data.py`	Root	Auto-generated module with `VARIATION_DATA`, public API functions
`MountModel.variation`	`editor/mount_model.py`	Read/write property with per-type validation
Appearance dropdown	`editor/overview_tab.py`	Identity section, row 4
`test_variation.py`	`tests/`	36 tests: data API, model, swap reset, labels, edge cases

Public API (`variation_data`)

from variation_data import (
    get_variations,          # Full variation dicts for a type
    get_variation_count,     # Number of variations (0 for single-appearance)
    get_variation_labels,    # Formatted labels for dropdown
    get_variation_label,     # Single label by index
    has_variations,          # True for Buffalo/Moa/Wolf
    validate_variation_index,# Bounds check
    get_rarity_tier,         # Weighting → rarity string
)