Throughout the Dark Souls games players fight an enormous number of bosses. Some of these bosses are more frustrating than others, sure, but most of them have weaknesses that can be taken advantage of. These weaknesses usually make sense - Gravelord Nito is weak to Fire damage, which makes sense as he has no connection to Fire or the First Flame.
Other times, Dark Souls boss weaknesses make much less sense. Among the more famous of these discrepancies is that Gwyn, the Lord of Sunlight, the final boss of Dark Souls, is weak to Fire – but he wields a flaming sword and was the very person who linked the First Flame long ago. Gwyn's nonsensical weakness is but one of many that stick out throughout the series.
DS1: Gwyn, Lord of Sunlight, Is Weak to Fire
In the original Dark Souls the player journeys through Lordran in the effort to collect the great souls of Lords Gravelord Nito, the Witch of Izalith, Seath the Scaleless, and of course Gwyn, the Lord of Sunlight. Gwyn is a central character in the overarching Souls series as without his choices the Linking of the Fire Flame would have never happened in the first place.
Humanity is tied to the Dark, after all, as the furtive pygmy found the Dark Soul in the first flame while Gwyn found the Light. But Gwyn isn't weak to Dark damage, he's weak to Fire damage, albeit only a little bit. Maybe this has something to do with burning his body away to link the fire, but one would think that the person who staved off the Age of Dark would not be weak to the very tool he used to extend the Age of Fire.
DS2: The Covetous Demon Is Weak to Fire
Demons in the Souls games are linked to the Witch of Izalith and their attempt to manifest life with the Lord Soul they found in the First Flame. Demons were created when the Izalith Witches lost control of the Chaos Flame and it spurred forth its own form of twisted life - while Nito has the Lord Soul of death, the Witch of Izalith found the Lord Soul of life.
However, in Dark Souls 2, the Covetous Demon encountered in Earthen Peak is weak to Fire, despite just about every other Demon in the series being resistant to it. This may be because the Covetous Demon may not have come from the same source of other Demons, though. The Covetous Demon is described as having once been a man whose "deep affections were unrequited," so he transformed into what we encounter in-game.
DS3: The Nameless King and King of the Storm Are Weak To Lightning
The Nameless King and his mount, the King of the Storm, are the final bosses of Archdragon Peak in Dark Souls 3. The Nameless King is nameless because it was struck from record by Gwyn, who wanted to rid all knowledge of his first-born son. As such, the Nameless King is tied to Lightning, while Everlasting Dragons are typically weak to it.
After dismounting the King of the Storm in the transition cutscene, the Nameless King on his own is resistant to Lightning. Even while riding his King of the Storm, though, he apparently doesn't or can't extend that same resistance to his flying partner. One would think that allying with the Dragons over Gwyn would lead to the Nameless King working on ways to circumvent their resistance to Lightning, or that he would at least cast some sort of buff on the King of the Storm.
DS2: The Old Dragonslayer Is Not Weak To Anything
The Old Dragonslayer is one of two bosses found in Heide's Tower of Flame, one of Dark Souls 2's earliest areas. Dark Souls fans taking on the sequel may be surprised to learn that the Dragonslayer Ornstein shows up at this practically beginning-of-the-game area. However, it's heavily implied not to be the real Ornstein, but rather someone else who took heavy inspiration from the legendary Knight of Gwyn.
Because of this, the Old Dragonslayer ought not to have nearly the strength of Ornstein, and this proves to be the case as the Bearer of the Curse doesn't have much trouble killing this impostor. Though Ornstein himself is weak to Fire in Dark Souls, somehow the Old Dragonslayer gets away with having no weaknesses despite not coming close to the prowess of his inspiration.
DS1: Pinwheel Is Weak To Everything
Pinwheel is a boss in Dark Souls with one of the more interesting and personal backstories. A Necromancer, Pinwheel attempted to steal the power of Gravelord Nito to bring back his wife and child, only to have the spell go awry and graft them onto his own body instead as a single living being.
However, it doesn't make sense for a boss with such an amazing backing track, such rich lore, and such a unique moveset to be killable in just a few hits. No other boss in Dark Souls is so blatantly weak, and it doesn't make sense that Pinwheel gets the smallest health pool of the lot, especially considering how relatively late in the game players are expected to come across him. Pinwheel is certainly far from the most fearsome foe players fight in the Souls games, but he deserved better representation.
Dark Souls is available now for PC, PS3, PS4, PS5, Switch, Xbox 360, Xbox One, and Xbox Series X/S.