Here’s another monster I never heard of, though I’m almost sure they come from a previous edition. They’re on the Monster Manual only.
Like Bodaks, Boneclaws are constructed undead that don’t occur naturally. Lots of necromantically inclined villains (liches, Orcus priests and the like) use them as guards and assassins. Creating one involves building a body from corpse parts and binding an evil soul into it through magic. The result is a Large Shadow Animate (undead), with variable-length talons that can reach 10 feet in length at maximum extension.
The ritual for creating a boneclaw is one of those “secrets” that keeps being stolen and traded away all the time. Some people say it was first developed by Vecna himself, though the true authors are a coven of hags led by the night hag Grigwartha. Her version of it used the corpse of an ogre and the soul of an oni, but others have adapted it for different “raw materials”. Grigwartha frequently traded the ritual for favors from other necromancers, so if you want your current villain to have access to boneclaws you don’t need any special explanation for it.
This entry has only a single variety, appropriately named Boneclaw. It’s a Level 14 Soldier with 136 HP and the usual undead traits of immunity to disease and poison plus Resist 20 necrotic and Vulnerable 5 Radiant. It’s far from mindless, with Int 10 and an Evil disposition. It speaks Common, and runs at you with Speed 8.
The boneclaw attacks with its claws (duh), which have Reach 3 and Threatening Reach. If a boneclaw hits someone with an opportunity attack, it can make another opportunity attack against the same target in the same turn. A nasty surprise to people who think they’re safe after the first one.
When bloodied, it lets out a Necrotic Pulse in a Close Burst 10, healing undead allies by 10 points and damaging living enemies by the same amount.
A relatively simple yet flavorful monster, whose flavor is further enhanced by whomever you partner it with. The sample encounter is level 14, a lich and its complement of bodyguards: two boneclaws and a shield guardian.
If you want to build a custom boneclaw, an assassin version that’s a Lurker or Skirmisher instead of a Soldier might be appropriate. Other than the undead resistances, the signature trait here seems to be the long Reach on the claws and doing something necrotic when it’s bloodied.