Add to a creature's drop list without replacing it

This example is based on the author's ResourcesAndLoot mod. Its DT_LootDropTable edits use $Append under each creature's row. We will add one resource-drop entry, then show a separate way to tune an existing entry.

This is a raw DataTable change. It is not a new creature, a spawn definition, or an instruction to copy all of an exported loot table.

1. Trace the creature to the table and row it uses

In FModel, inspect the creature and follow its loot reference. The example uses:

• table: /Game/Gameplay/Items/LootDropTables/DT_LootDropTable.DT_LootDropTable;
• row: AbyssalDemon;
• array field: Resources;
• item: /Game/Gameplay/Items/Resources/Animal/ITEM_Resources_Abyssal_Ashes.ITEM_Resources_Abyssal_Ashes.

Those names are present in the author's installed files and the runtime's loot lookup. They are not a promise that every creature uses this table, or that every game build keeps the same rows. Variants such as AbyssalDemon_Child are separate rows; changing one does not automatically change the other.

2. Understand the relevant export

This trimmed, reconstructed export-shaped fixture keeps the relevant table/row shape and the drop fields from the author's file. It is not a complete or verbatim vanilla drop table:

// Reconstructed excerpt of a DataTable export, not a complete vanilla table.
// Row/drop fields and reference come from the author's ResourcesAndLoot file.
[
  {
    "Type": "DataTable",
    "Name": "DT_LootDropTable",
    "Rows": {
      "AbyssalDemon": {
        "Resources": [
          {
            "SpawnedItemData": {
              "ObjectName": "ItemData'ITEM_Resources_Abyssal_Ashes'",
              "ObjectPath": "/Game/Gameplay/Items/Resources/Animal/ITEM_Resources_Abyssal_Ashes.0"
            },
            "MinimumDropAmount": 1,
            "MaximumDropAmount": 1,
            "DropChance": 5.625,
            "bOneInstancePerPlayerOnlyVisibleToThem": false,
            "bAutoAddToInventory": false,
            "bOnlyForPlayersThatInflictedDamage": false
          }
        ]
      }
    }
  }
]

The outer export list and Type/Name identify the exported table. Rows contains row names; AbyssalDemon.Resources contains drop structs. For a mod, replace those export wrappers with the actual loader's table/row target.

The exported ObjectPath ends in .0. Combined with ObjectName, it refers to the named item export. Our hand-written patch uses the inspected complete object-path string instead. Do not infer item identity from a display label.

3. Write an additive, existing-row-only patch

Create MoreAbyssalDrops/raw/10-add-drop.jsonc:

{
  "$Patch": "/Game/Gameplay/Items/LootDropTables/DT_LootDropTable.DT_LootDropTable:AbyssalDemon",
  "$Target": {
    "$Append": {
      "Resources": [
        {
          "SpawnedItemData": "/Game/Gameplay/Items/Resources/Animal/ITEM_Resources_Abyssal_Ashes.ITEM_Resources_Abyssal_Ashes",
          "MinimumDropAmount": 1,
          "MaximumDropAmount": 1,
          "DropChance": 5.625,
          "bOneInstancePerPlayerOnlyVisibleToThem": false,
          "bAutoAddToInventory": false,
          "bOnlyForPlayersThatInflictedDamage": false
        }
      ]
    }
  }
}

Lines	Meaning
2	$Patch names one existing row as full-table-object-path:RowName. It must resolve; it is not a request to create a row if the name is misspelled.
3	$Target contains only the changes for that existing row.
4–5	$Append.Resources adds struct entries to the current array, preserving its existing entries. Capitalization matters.
7	SpawnedItemData references an existing, mounted and valid item. A missing item's name cannot manufacture it.
8–9	Minimum and maximum amounts belong to this added drop entry. Keep minimum no larger than maximum.
10	DropChance is the native field/value used in the source mod. Its unit must be established for this row type; it is not interchangeable with another struct's ProbabilityOfDrop.
11	The native per-player visibility option is deliberately false in this example.
12	The item is not automatically inserted into inventory by this option.
13	The native damage-participation restriction is deliberately false here.
Remaining lines	Close the new entry, append array and patch envelope. No other table rows are supplied.

The source mod uses 5.625 for this field. This guide preserves that value rather than claiming a measured drop percentage. Do not translate it to 0.05625, or promise a rate to players, without verifying the game's native semantics and actual rolls. Resource destruction/consumable drop structs in the same mod use different names such as ProbabilityOfDrop and MinToDrop. Copying those field names into this row would target the wrong layout.

4. Know what append does—and does not do

$Append does not deduplicate by item path. If the row already contains the same item, you may add another independent drop entry. Loading two mods that append the same entry can do the same. Inspect the original and other enabled mods before choosing append.

Do not replace the wrapper above with:

// Replacement example only: this discards other Resources entries.
{
  "Resources": []
}

A normal array assignment replaces that array. Supplying a shortened copied list does not mean "only change the entries shown." An empty array means an empty array, not "leave it alone."

5. Tune one existing drop instead

Use a separate, later compatibility mod when the entry already exists once:

// This edits an existing unique drop. It does not add a missing drop.
{
  "$Patch": "/Game/Gameplay/Items/LootDropTables/DT_LootDropTable.DT_LootDropTable:AbyssalDemon",
  "$Target": {
    "Resources": {
      "$Patch": [
        {
          "$Match": {
            "SpawnedItemData": "/Game/Gameplay/Items/Resources/Animal/ITEM_Resources_Abyssal_Ashes.ITEM_Resources_Abyssal_Ashes"
          },
          "$Target": {
            "MinimumDropAmount": 2,
            "MaximumDropAmount": 3
          }
        }
      ]
    }
  }
}

The outer $Patch still selects the table row. The inner Resources.$Patch selects one struct-array member with $Match.SpawnedItemData. Its $Target changes only that entry's amount fields, leaving its chance, flags and the other drops unchanged. A missing or ambiguous match rejects that array patch; it is not a fuzzy search or an add-if-missing operation.

For array matching, object references must use the supported path-string form, not the whole FModel ObjectName/ObjectPath wrapper. If several entries use the same item, add other stable, reflected scalar fields to the selector only when they identify the intended entry unambiguously. Avoid $Index unless you control the exact list and understand how earlier mods can reorder it.

Choose add or tune deliberately. If you test both example mods, place TuneAbyssalDrops after MoreAbyssalDrops and ensure there is exactly one matching entry. Test the two together before sharing them as a combined loot preset.

6. Verify a real drop, not just a loader summary

1. Enable the chosen folder in mods/runeschema.txt and fully restart.
2. Inspect Diagnostics for the exact table, row and property failures.
3. Confirm the creature variant actually consumes the row you edited.
4. Test the normal kill/loot path in a disposable world. A manually granted item proves availability, not that the loot system rolled it.
5. Check that original drops remain and that no duplicate entry was added.
6. Use enough trials to evaluate probability; one kill cannot establish a rate.
7. Test host/client ownership, visibility and inventory options separately.

The raw reference covers full paths and row creation. Patch operators explains the two meanings of $Patch used above and the different DataAsset operation form.