Added ComboDice modifier for dice rolls

module/dice/die/baseDie.mjs

@@ -0,0 +1,31 @@
+import { adjustDice } from '../../helpers/utils.mjs';
+
+export default class BaseDie extends foundry.dice.terms.Die {
+    static MODIFIERS = {
+        ...foundry.dice.terms.Die.MODIFIERS,
+        c: 'comboDice'
+    };
+
+    async comboDice(modifier) {
+        /* ComboDice only works with exactly two dice and both have to be the same denomination */
+        if (this.number !== 2) return false;
+
+        const maxIncreasesDiceSize = modifier.endsWith('1');
+        return this.continueCombo(maxIncreasesDiceSize);
+    }
+
+    async continueCombo(maxIncreasesDiceSize) {
+        const lastIndex = this.results.length - 1;
+
+        /* The Combo only continues if the latest roll was higher than the previous */
+        if (this.results[lastIndex].result <= this.results[lastIndex - 1].result) return false;
+
+        const increaseDiceSize = maxIncreasesDiceSize && this.results[lastIndex].result === this.faces;
+        const denomination = increaseDiceSize ? adjustDice(this.denomination, false) : this.denomination;
+        const newRoll = await (new Roll(`1${denomination}`)).evaluate();
+        this.results.push({ result: newRoll.total, active: true });
+        this.number += 1;
+
+        return this.continueCombo();
+    }
+}