mark all entities spawn by the plugin and allow other plugins to check for that

src/main/java/me/youhavetrouble/standin/converter/ArmorStandToMannequinConverter.java

@@ -27,8 +27,9 @@ public class ArmorStandToMannequinConverter implements EntityConverter<ArmorStan
     public Mannequin spawn(@NotNull ArmorStand from) {
         try {
             return from.getWorld().spawn(from.getLocation(), Mannequin.class, (mannequin -> {
-                mannequin.customName(from.customName());
+                markAsTransformed(mannequin);
                 EntityConverter.saveRawEntityName(mannequin, EntityConverter.getRawEntityName(from));
+                mannequin.customName(from.customName());
                 mannequin.setImmovable(!from.canMove());
                 mannequin.setGravity(from.hasGravity());
                 for (EquipmentSlot slot : EquipmentSlot.values()) {

src/main/java/me/youhavetrouble/standin/converter/EntityConverter.java

@@ -1,5 +1,6 @@
 package me.youhavetrouble.standin.converter;
 
+import me.youhavetrouble.standin.StandIn;
 import net.kyori.adventure.text.Component;
 import net.kyori.adventure.text.serializer.plain.PlainTextComponentSerializer;
 import org.bukkit.NamespacedKey;
@@ -26,6 +27,11 @@ public interface EntityConverter<F extends Entity, T extends Entity> {
      */
     T spawn(@NotNull F from);
 
+    default void markAsTransformed(@NotNull T entity) {
+        PersistentDataContainer pdc = entity.getPersistentDataContainer();
+        pdc.set(StandIn.KEY, PersistentDataType.BYTE, (byte) 1);
+    }
+
     /**
      * MiniMessage serialized entity name
      * @param entity Entity to get name for

src/main/java/me/youhavetrouble/standin/converter/MannequinToArmorStandConverter.java

@@ -26,6 +26,7 @@ public class MannequinToArmorStandConverter implements EntityConverter<Mannequin
     public ArmorStand spawn(@NotNull Mannequin from) {
         try {
             return from.getWorld().spawn(from.getLocation(), ArmorStand.class, (armorStand -> {
+                markAsTransformed(armorStand);
                 armorStand.customName(from.customName());
                 EntityConverter.saveRawEntityName(armorStand, EntityConverter.getRawEntityName(from));
                 armorStand.setGravity(from.hasGravity());

src/main/java/me/youhavetrouble/standin/entity/EntityHandler.java

@@ -8,6 +8,7 @@ import io.papermc.paper.registry.data.dialog.body.DialogBody;
 import io.papermc.paper.registry.data.dialog.input.DialogInput;
 import io.papermc.paper.registry.data.dialog.input.SingleOptionDialogInput;
 import io.papermc.paper.registry.data.dialog.type.DialogType;
+import me.youhavetrouble.standin.StandIn;
 import me.youhavetrouble.standin.converter.EntityConverter;
 import net.kyori.adventure.text.Component;
 import net.kyori.adventure.text.event.ClickCallback;
@@ -172,4 +173,13 @@ public abstract class EntityHandler<E extends Entity> {
         CHANGE_TYPE,
     }
 
+    /**
+     * Checks if entity is entity transformed by stand-in plugin
+     * @param entity entity to check
+     * @return boolean representing whether entity is a stand-in entity
+     */
+    public static boolean isStandinEntity(@NotNull Entity entity) {
+        return entity.getPersistentDataContainer().has(StandIn.KEY);
+    }
+
 }