The object of research is an approach of functionality extension for simulation toolkits based on iFogSim. It is assumed by the native approach that enhancement of functionalities should be achieved by inheriting the fog device class and defining new features in its body. However, this approach makes it impossible to use inherited simulators together and significantly decreases flexibility even when utilizing a single simulator. Another problem related exclusively to iFogSim is a specific communication scheme between application modules, which results in data routing limitations in fog architectures and odd data streams taken into account. This paper introduces an alternative extension approach incorporating a peculiar inheritance scheme which tries to reconsider the standard approach from a behavioral design patterns point of view. The key feature of the suggested approach is an extraction of fog device features from the native class into separate behavioral classes. Meanwhile, the designed inheritance scheme allows to flexibly override and combine behaviors. According to the approach principles the developed simulator extends iFogSim with application modules addressing capabilities solving limitations, along with implementing users’ mobility and dynamic wireless connectivity as it is done in MobFogSim. With the aim to check its correctness, the designed toolkit was validated with the standard for iFogSim case study of «EEG Tractor Beam game» application. The validation included four scenarios. In the first two scenarios the features of users’ mobility and dynamic base station connectivity were validated. And in the next scenarios that utilized address routing the obtained delay and network usage values were compared with theoretically calculated ones. The validation results indicated the correct simulator behavior, and introduced functionalities extension approach, being more complex in comparison with the inative one, can significantly improve flexibility of the simulator