Final answer:
The gnome Umbriel's journey to the Cave of Spleen in Canto 4 of the poem is a parody of the epic convention of Supernatural beings.
Step-by-step explanation:
The gnome Umbriel's journey to the Cave of Spleen in Canto 4 of the poem is a parody of the epic convention of Supernatural beings. In epic poetry, supernatural beings often play a significant role or have special powers. In this parody, Umbriel represents a supernatural figure, traveling to the cave where Belinda's bad humor resides.