While Elio doesn't have a specific theme song in mind, his genre would definitely be Lo-Fi Hip-Hop to ideally embody his personality and aesthetics - especially if it's accompanied by background lyrics like most Villain Team Boss themes (i.e. Guzma, Ghetsis, Rose).

For example, this would be his encounter theme in the Pokemon Overworld, which instantly alerts other players and NPCs of his vibes: (https://www.youtube.com/watch?v=aWWAIV3dzKk)