What are the poetic devices used in the famous poem "Ozymandias" by Percy Bysshe Shelly?

The first device used by the poem is the formal one of rhyme and meter. The poem is written in the form of a sonnet, albeit with a slightly irregular rhyme scheme. The lines of the poem are written in the meter of iambic pentameter, meaning that each line has five feet, with each foot consisting of a weak followed by a strong syllable. The rhyme scheme is an odd hybrid of a Shakespearean octave and Petrarchan sestet, with minor variations; the actual rhyme pattern is  ABAB ACDC EDEFEF

There are a few instances of alliteration in the poem, including "cold command" and a fair amount of sibilance:  "stone ... Stand ... sand ... sunk  ... sneer ... sculptor ... survive ... stamped."

We have two instances of synecdoche, in which the part stands for the whole, as "hand" and "heart" are used to stand in for elements of Ozymandias' character.

Finally, there is the irony of the grandeur of the inscription on the pedestal and the current state of decay of the sculpture itself and the kingdom over which Ozymandias ruled.