Mari is a philologist and a connoisseur of science fiction (see his poetic essay "Le copertine di Urania" in Tu, sanguinosa infanzia, 1997) and comics.
the story "I palloni del signor Kurtz", in Euridice aveva un cane, 1993); other important motifs are the obsession for other people's life that one could not live (in the short story "Euridice aveva un cane", 1993, or in Rondini sul filo, 1999), of literature as ersatz life, of memory and its workings (Verderame, 2007).
Mari intensely dislikes change, so he mistrusts modernity in its more vulgar and showy aspects; he is fascinated by obsessive personalities (Walter Benjamin in Tutto il ferro della Torre Eiffel, Roger Waters in Rosso Floyd); he nonchalantly mixes fact and fiction in his works, both in those with an overwhelming autobiographic component (Rondini sul filo, Tu, sanguinosa infanzia, Filologia dell'anfibio), and in those novels where he uses, like a puppeteer, historical characters (Benjamin and Marc Bloch - plus countless other writers and artists - in Tutto il ferro della Torre Eiffel, the Italian romantic poet Giacomo Leopardi in Io venia pien d'angoscia a rimirarti, the members of the Pink Floyd band in Rosso Floyd).
He has a style similar to that of other Italian fiction writers like Carlo Emilio Gadda, Tommaso Landolfi and Giorgio Manganelli, and also the French author Louis-Ferdinand Céline (especially in Rondini sul filo).
Mari is also a poet (Cento poesie d'amore a Ladyhawke, Einaudi 2007) and an academic scholar (his essays include L'Iliade di Vincenzo Monti, 1982; Venere celeste e venere terrestre, 1988; Momenti della traduzione fra Settecento e Ottocento, 1994; Il genio freddo: La storiografia letteraria di Girolamo Tiraboschi, 1999); he also wrote essays on European and American fantastic literature (I demoni e la pasta sfoglia, Quiritta 2004).