Fiend

Fiend is a catch-all name used to collectively refer to any and all of the malevolent entities that could hail from a game's equivalent of the Lower Planes. It is a nondiscriminatory term that encompasses both races such as Demon, Devil and Daemon (or other "Evil Outsiders") as a whole, and the myriad sub-varieties of each of those races.

Fiend was popularized as a catch-all thanks to the Dungeons & Dragons setting of Planescape; motivated on the meta-level by the dread Satanic Panic, in-universe, it was a polite term that planars came up with in order to avoid attracting angry "corrections" from either Tanar'ri or Baatezu, who both looked similar and absolutely despised being mistaken for each other, given their races were locked in the Blood War.

The new 5E edition of Spelljammer features a new type of Fiend: SPACE CLOWNS! These reality-warping monsters come from a system known as Clown Space, formed from 3 Ring Worlds (a pun on "3 Ring Circus"). They're a homage to the cult classic 1988 Sci-Fi Horror Comedy Film "Killer Klowns from Outer Space". Much like the murderous clowns in the film, these guys have reality-warping powers based on clown gags.