If there is one single calling card that could encompass the entire Dark Souls series, it would almost certainly be a reference to boss battles. FromSoftware has gone from a relatively fringe developer to being one of the top AAA developers in the world in large part due to their willingness to craft lots of brutally challenging boss fights for their players to overcome.

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Dark Soulsput this style of game on the map (although it all began with Demon's Souls) and to this day many of the series' boss battles are legendary. However, that doesn't mean that they're all mandatory. In fact, FromSoftware likes to stash some of their most challenging bosses in areas that players don't even need to find before finishing the game. Just because these bosses are optional doesn't mean they won't make for worthy challenges.

10 Moonlight Butterfly - Dark Souls

The Moonlight Butterfly lurks in the recesses of the Darkroot Garden

The Moonlight Butterfly's difficulty is weighted heavily by the RNG that players face while fighting it on any given run. Between its laser beam attack and its charge-up AOE while perched on the arena's bridge, this boss can easily wipe out a player's health in a matter of seconds.

Maybe the hardest aspect of this boss is its arena: a thin stone bridge with doors at either end and the player trapped in the middle. It's very easy to tumble off the bridge accidentally, and because the Moonlight Butterfly hangs around the fringes, locking onto it can throw off the direction of a dodge roll and send players falling to their deaths.

9 Lud & Zallen - Dark Souls 2

Lud & Zallen are the other two pets of the Ivory King

By the midway point of the Crown of the Ivory King DLC, around the time when they discover the Frozen Wastes, players will have already fought Aava, The King's Pet. So of course, the next step is to fight the King's other two pets at the same time.

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Lud & Zallen can be found in the furthest reaches of the Frozen Wastes. When players get Lud's health down to 50%, Zallen will appear. Zallen has a berserk attack that will regenerate its health and increase its damage. It's a heck of a time, although not nearly as difficult as surviving the Frozen Reindeer that litter the path leading up to this fight.

8 Capra Demon - Dark Souls

The Capra Demon and his hounds can corner players in an instant

The Capra Demon becomes a bit of a pushover once players know the trick to beating him, but prior to that, when they first wander into his painfully small arena, this boss can be a nightmare. Ask any Dark Souls veteran and they'll tell you, it's not just the Capra Demon himself, it's the dogs.

Two of them, specifically, will charge players the second they cross through the boss' fog wall. It's an immediate distraction from the boss, who also begins closing ground quickly but can get lost in the background. The trick, now widely known, is to run past all three and up the stairs at the back of the room. It's the only way to separate the dogs from the boss and deal with them one-on-one.

7 Sir Alonne - Dark Souls 2

Sir Alonne has an army named after him

Many of the most epic fights in the Dark Souls series play out against giant monsters whose sheer size makes for an epic achievement when they're finally taken down. Sometimes though, a showdown between two warriors bearing nothing but swords and armor can be just as epic.

Enter Sir Alonne, found in the memory of the Old Iron King in Dark Souls 2's Crown of the Old Iron King DLC. Alonne is such a badass that the Iron King named his army after him, and this fight reinforces that decision. Alonne is fast, skilled, and capable of parrying the player's attacks with ease. This fight is a true test of skill in a way that few are and awards a special death animation to players who defeat Alonne without taking damage.

6 Champion Gundyr - Dark Souls 3

Champion Gundyr should not be taken lightly

Players encounter this boss' first incarnation at the conclusion of Dark Souls 3's tutorial, and when they stumble upon him again in the game's late stages, that familiarity may cause them to take this fight lightly. That will prove to be a mistake, likely around the time when Champion Gundyr crushes them beneath his halberd.

Here players are fighting Gundyr at the height of his abilities. He moves faster, hits harder, and is generally far more aggressive than his corrupted counterpart Iudex Gundyr. This fight will strain even the most experienced players, all the more so with the awareness that they've already defeated this warrior ringing in their minds as Champion Gundyr schools them repeatedly.

5 Black Dragon Kalameet - Dark Souls

Black Dragon Kalameet must be shot out of the sky before players can fight him

There's nothing like a good dragon fight, and Black Dragon Kalameet gives players exactly that. The build-up to this boss alone makes for an epic showdown once the fight finally happens. Kalameet is visible in the sky multiple times before the fight, yet he cannot be damaged. Players will have to enlist Hawkeye Gough and his massive bow to shoot Kalameet out of the sky, and that's just so the battle can begin.

Once grounded, Kalameet is a force. His attacks come in wide swings and slams that are difficult to dodge, and his black flame attacks cover huge swaths of the arena in fire. He can also take to the air and attack in flight, which only adds to the challenge. There is no perfect tactic for this fight. Players should come prepared with as much Estus as they can, because they may be fighting for a while.

4 Darklurker - Dark Souls 2

Darklurker likes to make copies of itself

One of the most unique bosses in the series, Darklurker can only be accessed by joining the Pilgrims of Dark covenant and clearing out three Abyssal Dungeons. Then players will have to return to Darkdiver Grandhal to access the Darklurker fight.

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The Darklurker looks like it was pulled straight from a Diablo cutscene. Equal parts angelic and monstrous, it primarily uses soul magic attacks but has a few abilities that make it stand alone. For one, it can turn invisible, but it can also teleport and will create a copy of itself at around 50% health. Once there are two Darklurkers the fight becomes frantic as players try to attack one of them while avoiding the other.

3 Darkeater Midir - Dark Souls 3

Darkeater Midir can cover the whole arena in flame

Found in The Ringed City DLC of Dark Souls 3, Darkeater Midir may be the most difficult dragon fight in the Dark Souls series. His attacks come in fast and hit very hard, a number of them are painfully difficult to avoid, and to top it all off he has a massive health pool to work through.

The worst attack of all is Midir's airborne flame breath. He'll take to the air and then spit a gout of flame straight down as he soars over the arena. The flames hit the ground and spread outward. There is no surefire way to avoid this attack, so the best option is to wear as much fire-resistant gear as possible, and then hope Midir doesn't rely on it too much.

2 Nameless King - Dark Souls 3

The Nameless King is Fire Lord Gwyn's lost child

Found in Archdragon Peak - an optional area in Dark Souls 3 - the Nameless King is an incredible boss fight both for the moment-to-moment gameplay and for the lore implications that he carries for the entire Dark Souls series. Right from the moment he swoops down on his huge feathered dragon, it's clear that he's a formidable foe.

The fight's first phase is challenging, but nothing noteworthy. Once the Nameless King's dragon is killed and he absorbs its power - becoming the King of the Storm - the fight becomes nightmarish. He attacks so quickly, launching from one end of the arena to the other. He creates lightning shockwaves that dart along the ground and can send lightning strikes crashing down on the player. It's a challenge for players just to stay alive while fighting him, let alone trying to land attacks of their own.

1 Smelter Demon - Dark Souls 2

The Smelter Demon fight is pain, enough said

Most Dark Souls 2 players remember this guy, and they aren't good memories. The Smelter Demon is a painful fight. He's huge, he hits hard, and his defenses make the damage players dish out negligible. It takes a lot of work just to hurt this boss, that's without even the process of avoiding his various attacks.

At 60% health, the Smelter Demon will "stoke his fire," lighting his chest aflame which deals AOE fire damage whenever the player gets close. Then at 50% health, he'll light his sword on fire, increasing his damage. Thankfully, this fight can be avoided entirely, the downside being that the Smelter Demon guards the only mid-level Bonfire found in the Iron Keep.

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