Discuss the formal aspects of 'mask of anarchy' in terms of voice, diction, rhyme scheme, meter and figurative language. What are some of the Romantic characteristics of the poem?

Shelley's poem is an allegorical commentary on political events in England, particularly the Peterloo Massacre of August 16, 1819. Written in 91 stanzas, the poem is written in trochaic tetrameter with an AABB rhyme scheme, although many of the lines contain only seven syllables and end on a stress.
The poem describes the coming of the figure of Anarchy to London. The allegorical nature of the poem allows Shelley to describe the political situation in England using heightened language:

Last came Anarchy; he rode On a white horse, splashed with blood; He was pale even to the lips,Like Death in the Apocalypse

Anarchy is, of course, the British government ("And he wore a kingly crown / And in his grasp a sceptre shown"), which had brutally put down a protest for democratic reform at Peterloo. The specter of Anarchy is opposed by the figure of Hope ("a maniac maid, / And her name was Hope, she said: / But she looked more like Despair;").
The Romantic elements of the poem include, of course, the championing of the common people over aristocrats, the use of supernatural or mythic figures to represent current events, and the reliance on emotion and emotionally charged imagery to make his point. While many had died at Peterloo asking for electoral reform, in Shelley's poem the forces of Anarchy are defeated by the "mist" of freedom:

As flowers beneath the footstep waken, As stars from night's loose hair are shaken, As waves arise when loud winds call, Thoughts sprung where'er that step did fall.And the prostrate multitudeLooked—and ankle deep in blood,Hope, that maiden most serene,Was walking with a quiet mien:And Anarchy, the ghastly birth, Lay dead earth upon the earth;

Shelley's poem was meant to be a kind of emotional call to arms on behalf of democracy, but it did not appear in print until 1832, due to government censorship of political dissent.