In Doctor Faustus, Wagner is every inch the stock character of the clever, wily servant. But he departs from this stock character in one very important respect. Whereas most wily servants in plays disrespect their masters and mistresses, spending a great deal of time trying to deceive them, Wagner actually respects Faustus and tries to emulate him.
In his effort to emulate Faustus, Wagner sets about obtaining a servant of his own. Because he is not possessed of the same demonic power as Faustus, he initially goes about this through trickery and deceit. But Wagner has been watching Faustus closely, and he follows his master's example by conjuring up two devils to scare his would-be servant, Robin, into signing the deal.
That a humble servant is able to perform the same feats of magic as Faustus would suggest that such magic is less otherworldly than previously suggested. Faustus comes to much the same conclusion, frustrated as he is that he has become little more than a glorified magic act, performing for the entertainment of the world's rulers—or tricking them, as the case may be.
Wagner's conjuring up of the two devils raises the question of whether it was really worthwhile for Faustus to sign his soul away. Wagner's abilities are less than Faustus's, but Wagner didn't have to sell his soul to the Devil to perform this particular feat of magic.