Spell04 Dynamic Scaling

Part 4: Dynamic Scaling Spells (Play Other Cards)

← Part 3: Unit Stat Upgrades | Next: Part 5: Card Triggers →

In this lesson, we explore dynamic scaling—effects that calculate their magnitude based on statistics tracked during combat.

We will create Play Other Cards, a 2-Ember spell that grants a target unit +2 Attack for every card played during the current battle. You will learn how CardTraits modify upgrades and how to configure tracked statistics.

---

1. Asset Setup

Download the custom card art:

• Download Art: PlayOtherCardsSprite.png
• Save Location: Save it to your mod project under textures/PlayOtherCardsSprite.png.

---

2. Complete JSON Definition

In Plugin.cs, add "json/spells/PlayOtherCards.json" to your AddMergedJsonFile call. Then create json/spells/PlayOtherCards.json and add:

{
  "$schema": "https://github.com/Monster-Train-2-Modding-Group/Trainworks-Reloaded/releases/latest/download/schema.json",
  "cards": [
    {
      "id": "PlayOthercards",
      "cost": 2,
      "names": {
        "english": "Play Other Cards"
      },
      "descriptions": {
        "english": "Apply +[trait0.power][attack] per card played this battle."
      },
      "rarity": "rare",
      "targets_room": true,
      "targetless": false,
      "class": "ClassBanished",
      "card_art": "@PlayOtherCardsCardArt",
      "pools": [
        "MegaPool"
      ],
      "traits": [
        "@PlayOtherCardsScalingTrait"
      ],
      "effects": [
        "@ApplyScaledUpgrade"
      ]
    }
  ],
  "effects": [
    {
      "id": "ApplyScaledUpgrade",
      "name": "CardEffectAddTempCardUpgradeToUnits",
      "target_mode": "drop_target_character",
      "target_team": "both",
      "param_upgrade": "@PlayOtherCardsUpgrade"
    }
  ],
  "traits": [
    {
      "id": "PlayOtherCardsScalingTrait",
      "name": "CardTraitScalingUpgradeUnitAttack",
      "param_tracked_value": "any_card_played",
      "param_entry_duration": "this_battle",
      "param_int": 2
    }
  ],
  "upgrades": [
    {
      "id": "PlayOtherCardsUpgrade",
      "bonus_damage": 0,
      "upgrade_will_be_scaled_by_non_magic_power_trait": true
    }
  ],
  "game_objects": [
    {
      "id": "PlayOtherCardsCardArt",
      "type": "card_art",
      "extensions": {
        "card_art": {
          "sprite": "@PlayOtherCardsSprite"
        }
      }
    }
  ],
  "sprites": [
    {
      "id": "PlayOtherCardsSprite",
      "path": "textures/PlayOtherCardsSprite.png"
    }
  ]
}

---

3. What’s New in This Recipe

Trait-Based Scaling Interception

Unlike traits have a keyword (such as CardTraitIgnoreArmor - Piercing), CardTraitScalingUpgradeUnitAttack does not add a Keyword to the card:

• It modifies the upgrade applied by @ApplyScaledUpgrade.
• It reads the tracked in-game statistic and adds tracked_stat * param_int to bonus_damage of the upgrade.

"traits": [
  {
    "id": "PlayOtherCardsScalingTrait",
    "name": "CardTraitScalingUpgradeUnitAttack",
    "param_tracked_value": "any_card_played",
    "param_entry_duration": "this_battle",
    "param_int": 2
  }
]

• param_tracked_value: Specifies the battle statistice to monitor ("any_card_played" increments every time any card is played).
• param_entry_duration: Sets the monitoring time window:
  • "this_turn": Gets the value of the statistic as of this turn. The value resets at the start of each new turn.
  • "previous_turn": Get the value of the statistic from the previous turn.
  • "this_battle": Gets the cumulative count of the statistic for the current battle (used here).
• param_int: The scaling multiplier (adds +2 attack per recorded event).

Important

Scaling traits of this type are specifically built for Spells. Attaching them to Monster cards can cause undefined behavior and bugs.

---

Upgrades as Scaling Templates

"upgrades": [
  {
    "id": "PlayOtherCardsUpgrade",
    "bonus_damage": 0,
    "upgrade_will_be_scaled_by_non_magic_power_trait": true
  }
]

• bonus_damage: 0: The default of any integer property is 0, so this could be left out, here for emphasis.
• upgrade_will_be_scaled_by_non_magic_power_trait: true: A flag for the upgrade that that this upgrade's parameters are modified by a scaling trait. This ensures that other mechanics that add upgrades to cards (like Reform) don't reset the scaled value back to 0.

---

Description Replacement Tokens

"descriptions": {
  "english": "Apply +[trait0.power][attack] per card played this battle."
}

• [trait0.power]: Dynamically pulls the param_int value (2) from the first trait (trait0) listed on the card.
• [attack]: Replaced by the Attack icon.

---

4. Testing Your Card

1. Build your solution and deploy the updated mod files to BepInEx/plugins/<YourMod>/.
2. Launch Monster Train 2 and verify no JSON errors appear in the BepInEx console log.
3. Start a battle with Play Other Cards in hand or deck:
   • Play several other cards first.
   • Inspect Play Other Cards: the dynamic description will update to show the current scaled attack buff.
   • Play it onto a friendly unit and verify that the attack gained matches (cards_played * 2).

---

Next Steps

Now that you can build dynamically scaled spells, continue to Part 5: Card Triggers (Pyre Sharpener) to build cards that activate automatically from hand without being cast.