It's time to build a better boss monster. No longer will you have to endure your players poking at your monsters' unearthedarcana
ankles until their hit points are whittled away, and the creature dies from a fatal blow to its big toe. Instead, your heroes can search a near-invincible foe for a weakness, try to exploit it, and fight hard to keep striking the monster where it hurts as it tries to protect its vulnerability. This house rule is great for gaming groups that want a more dynamic and thoughtful D&D combat experience—perhaps your group has very few combat encounters and you want them to be meaningful, or perhaps your game has lots of battles and you want your boss encounters to stand out from the trash mobs.
Because of the prevalence of weak point mechanics in video games like The Legend of Zelda, Shadow of the Colossus, and literally hundreds of other examples, this house rule may make your D&D game feel more like a game than a simulation of fantasy life. This doesn’t have to be the case: fantasy and mythology are flush with stories of legendary warriors and monsters with fatal physical flaws. Consider Achilles and his famous heel from The Iliad, the heavily armored Imperial walkers that could only be defeated by ensnaring their legs in The Empire Strikes Back, and the mighty dragon Smaug’s only vulnerability in The Hobbit.
Before using this house rule in your game, consider telling your players outright that your boss monsters will have a weak point that they can seek out to make defeating it easier.