Lycidas is considered to be the archetypal pastoral elegy in English; as a result, it embodies many of the characteristics of the pastoral. One of the major pastoral elements of the poem is that Milton disguises himself and Edward King (the friend for whom the poem was written) as "swains," or shepherds. Milton likens their life together at Cambridge to the life of the mythical shepherds, herding sheep and playing music. As a result, the whole poem is told through this pastoral "lens."
Another feature of the pastoral evident in the poem is its harmony with nature. After Lycidas dies, nature mourns him; the flowers all die, and the vines shrivel up. Similarly, they are brought forth in a beautiful catalog of flowers to decorate Lycidas's grave. The plants and nature seem to feel for Lycidas and the speaker, and to be active participants in the mourning.
However, an anomalous feature in Lycidas that doesn't fit within the traditional pastoral trope is the easy blending of pagan and mythical thought with Christianity: Milton's reference to "he who walks the waves" would be anachronistic for his ancient pastoral setting.