public override bool Execute(Npc npc, Character character) {
            if (!base.Execute(npc, character))
                return false;

            ItemTemplate template;

            // Check if user has all needed items.
            foreach(var t in NeededItemsList) {
                template = ItemManager.Instance.TryGetTemplate(t.Item1);
                if(character.Inventory.TryGetItem(template).Stack < t.Item2) {
                    character.SendInformationMessage(
                        TextInformationTypeEnum.TEXT_INFORMATION_MESSAGE, 0,
                        "Certaines conditions ne sont pas satisfaites.");

                    return true;
                }
            }

            // Check if user has the upgrade stone.
            template = ItemManager.Instance.TryGetTemplate(CoinParams.Item1);
            if (character.Inventory.TryGetItem(template).Stack < CoinParams.Item2) {
                character.SendInformationMessage(
                    TextInformationTypeEnum.TEXT_INFORMATION_MESSAGE, 0,
                    "Certaines conditions ne sont pas satisfaites.");

                return true;
            }

            // Take The Upgrade Stone.
            character.Inventory.RemoveItem(character.Inventory.TryGetItem(template), CoinParams.Item2);

            //Check if we have a success upgrade.
            if ((new Random().NextDouble() * 100) > Percentage) {
                character.SendInformationMessage(
                    TextInformationTypeEnum.TEXT_INFORMATION_MESSAGE, 0,
                    "L'upgrade a échoué!");

                return true;
            }

            // Upgrade Succeeded...
            character.SendInformationMessage(
                TextInformationTypeEnum.TEXT_INFORMATION_MESSAGE, 0,
                "Vous avez passé l'upgrade avec succes!");

            // Take items from user.
            foreach (var t in NeededItemsList) {
                template = ItemManager.Instance.TryGetTemplate(t.Item1);
                character.Inventory.RemoveItem(character.Inventory.TryGetItem(template), t.Item2);
            }

            // Give new items to user.
            foreach (var t in NewItemsList) {
                template = ItemManager.Instance.TryGetTemplate(t.Item1);
                character.Inventory.AddItem(template, t.Item2);
            }

            return true;
        }