Personification, the giving of human traits to non-human things, is all over this poem. Whether it is nature, Death, or inanimate objects, Shelley gives emotion to non-living things to show just how torn up everyone is over Keats' death. We're just surprised he didn't throw in a few talking animals for good measure.
Time is described as having several emotions, including sadness. Stanza I, line 4 describes the "Hour" as "sad." Stanza XLVIII (431) describes time as "decaying," as if it had a body. Stanza L (442) calls time "dull." The speaker's mourning of Keats' lack of time left on earth is transferred to time, as if it too was sorry to lose the youth.
Beginning in stanza III, Death is given human attributes. Line 27 has Death (made into a proper noun) "laughing at our despair." Stanza VII (55) describes Death as "kingly," but later says that she is "shamed" in stanza XXV by the presence of Keats' body. By giving Death a personality, Shelley is able to show that death is no match for the youth's eternal spirit.
Nature is personified all over this poem. In stanza XIV(126), the wind is "sobbing." Then we meet the Echoes, which in stanza XXII (195) are singing in grief, and Spring, which gets "wild" with grief in stanza XVI (136).
Throughout the poem, nature is portrayed as majorly mourning, mirroring the poet's own grief.