Fixed basic beastform

module/data/activeEffect/_module.mjs

@@ -0,0 +1,7 @@
+import beastformEffect from './beastformEffect.mjs';
+
+export { beastformEffect };
+
+export const config = {
+    beastform: beastformEffect
+};

module/data/activeEffect/beastformEffect.mjs

@@ -0,0 +1,18 @@
+export default class BeastformEffect extends foundry.abstract.TypeDataModel {
+    static defineSchema() {
+        const fields = foundry.data.fields;
+        return {
+            isBeastform: new fields.BooleanField({ initial: false })
+        };
+    }
+
+    async _preDelete() {
+        if (this.parent.parent.type === 'character') {
+            for (let item of this.parent.parent.items) {
+                if (item.type === 'beastform') {
+                    await item.delete();
+                }
+            }
+        }
+    }
+}