Retriever

The Retriever in Advanced Dungeons & Dragons is not a cute hairy doggy who can swim. This Retriever is a big hairy spider who will eat you.

They first showed up in Fiend Folio as a construct of Demogorgon himself; they are his invisible-stalkers, except very very visible. They are twelve-foot arachnoids, whose four forelimbs are as "cleavers" each inflicting 3d6 damage. They have six eyes, four of which fire sixty-foot LASER BEAMS, beholder-style: fire, cold, lightning, transmutation. Demons ride these things into battle sometimes, on "howdah".

The transmutation ray is fun: d4 says, mud, stone, gold, or lead. If gold or lead, the victim's friends will need that philosopher's stone from the eponymous JK Rowling book to turn him back again.

It seems this critter's designer wasn't in contact with E. Gary Gygax because, you'd think the Retriever would be ideal for Lolth's Demonweb Pits but it is not.

In 2e, Planescape brought them as enemies to the Tanar'ri, for Reasons. The edgelord module The Deva Spark features one. 3e elevated them to the full Monster Manual in the "Demon" section although still as constructs. Thus canonised as Open Content, Monte Cook put one in The Maze over in Beyond Countless Doorways.