Polymorphic electronics provides a new way for obtaining circuits that are able to perform two or more functions depending on the environment in which they operate. These functions can be activated under certain conditions by changing control parameters of the circuit (such as temperature, power supply voltage, light etc.). Existing polymorphic gates are difficult to use as building blocks in complex digital circuits. In this paper, some modifications of existing polymorphic gates are proposed in order to utilize them in non-trivial digital multifunctional circuits. The presented multifunctional circuits composed of these gates represent the most complex multifunctional circuits available nowadays. In particular, NAND/NOR and AND/OR polymorphic gates controlled by the power supply voltage are discussed and used in circuits such as the five-bit majority/ AND circuit and three-bit multiplier/six-bit sorting network circuit.