Much of the comedy in the play arises from the way Faustus's grandiose expectations of what access to the Devil's magical powers will bring him are betrayed. As always, what Mephistopheles promises turns out to be exaggerated, a hollow imitation of anything worth having. Faustus does not achieve the princely power he dreams of, but at best pulls off trifling mischief-making feats.
For example, magic allows Faustus to become invisible and hit the confused pope around the head. He also liberates Bruno, an enemy who the pope had imprisoned. He can conjure up ghostly forms of figures such as Alexander the Great and Darius and provide grapes for a duchess. He also plays cruel jokes on simple rural folk. But that is about as far as it goes.
Marlowe's point is that the devil is a liar who makes himself out to be much more powerful than he really is. Faustus thinks he is smart in aligning himself with the devil, but in the end, he is shown to be a fool who sells his soul for a few silly tricks.
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