Beastmen (40k)
Yes, once upon a time, Beastmen were playable in Warhammer 40,000. And then they disappeared. But now they have reappeared, with a mention in the core rulebook and a presence in the Heretics & Renegades army list printed by Forge World! Back in 3rd edition, Beastmen and other mutants were the byproduct of Genestealer Cults, which were a specific type of Genestealer infiltration, formerly called a Genestealer Clan, that started worshiping Chaos and the Ruinous Powers, thus becoming a Genestealer CULT. The army allowed for use of Genestealers, Beastmen, mutants and Demons. Later, the term Genestealer Cult was used for a general Genestealer infection, and the beastmen were shuffled off to the side in favour of a Genestealer Cult list having nothing to do with them, but that's fine as they then turned up in a playable mini-army in the Witch Hunters rulebook as an example of what the Witch Hunters fight against (called mutants in this case), and they also showed up again in the Eye of Terror codex, in the Witch Hunters case it's because mutations like that happen naturally in 40K, they're just usually killed when they're born and the army in question didn't follow the Imperium's teachings, and in the second case it was directly due to Chaos making a lot of mutants.
Now, they exist mainly in the fluff as a barely-tolerated strain of abhuman whose main use in the Imperial Guard is to act as meatshields so they can atone for being mutants. Some things never change.
