The Dark Souls series is not one known for its random events or chance encounters. Most areas are laid out the same way each time a player respawns, and while enemies roam their respective areas, there are almost none that will appear out of nowhere or by chance.
Rare encounters in Dark Souls aren't random, but there are moments and monsters in the game that most players will rarely experience. Some of the rarest enemies don't even respawn upon defeat, making them truly once-in-a-playthrough encounters. Others can be found down alternative paths, both in terms of areas and character builds.
9 Dark Souls: Evil and Good Vagrants
One of the few randomly occurring encounters in the entire Dark Souls series is the Vagrant, present in both an "Evil" and "Good" version. It's not known exactly how to force a Vagrant to spawn, but generally, they show up in areas of the game where lots of players die and leave behind lots of humanity.
The "good" version is white and will run away, while the "evil" version is red and will attack. If the Vagrant isn't killed, it will transfer to another player's world, literally wandering between worlds as if trapped between life and death.
8 Dark Souls: The Dreaded Basilisk
The Basilisk is an enemy found throughout the Dark Souls franchise that made its debut in the first entry. Their gigantic "eyes" and curse breath have made them one of the most feared and dangerous enemies in the franchise – in the first game, though, they are found very sporadically.
In the base game, the only time the player is forced to fight a Basilisk is in The Depths, although there are a few others in optional Great Hollow and the Ash Lake areas too.
7 Dark Souls: The Butchers
The Butchers are a pair of unique NPCs that don't respawn upon being killed. They show up in the Depths in a kitchen, and if the player sneaks up on them without raising suspicion, they will see them preparing lunch for the Depths' residents.
Both butchers are female, though they hide their faces behind a sack. The invading spirit Maneater Mildred wears a similar sack on her head, which has led some fans to speculate that the character is related to the two Butchers in the Depths.
6 Dark Souls 2: Getting Alsanna, Silent Oracle's Soul Early
Alsanna, the Silent Oracle, is an NPC only found in the Crown of the Ivory King expansion for Dark Souls 2. By giving her a massive 50 Loyce Knight souls, as well as killing the Burnt Ivory King boss fight, she will open a path that leads downwards.
She then grants the player her soul, which can be used to create a specialty sword, and a unique armor set. Players who don't mind a bit of rampant murder can snipe Alsanna from far away, which also gets her to drop her soul but not her armor set.
5 Dark Souls 2: Looking Glass Knight Allies
The Looking Glass Knight from the latter half of Dark Souls 2 had a unique mechanic that a limited number of players were able to take advantage of. By placing a Red Sign Soapstone anywhere in Drangleic Castle there is a chance that the player will be summoned by the Looking Glass Knight through its mirror shield to fight by its side.
Normally, the Looking Glass Knight summons ghostly allies through its shield about halfway through the fight. Summoned players are much harder to beat than NPC summons, but as the popularity of Dark Souls 2 dwindles over the years so too does the chance of actually encountering one of these turncoat players.
4 Dark Souls 2: Enraged Fume Knight
The Fume Knight is generally regarded as one of the most difficult bosses in the Dark Souls franchise, let alone just Dark Souls 2. The Fume Knight can actually be made more difficult, though, if the player chooses to wear Velstadt's helmet. Velstadt's helmet can be bought from Maughlin in Majula after spending 16,000 souls with the merchant and after defeating Royal Aegis Velstadt.
The Fume Knight and Velstadt had an ancient feud when the Fume Knight was known as Raime. He retreated to Brume Tower, became the Fume Knight, and apparently never forgot about his defeat at the hands of Velstadt.
3 Dark Souls 3: Champion Gundyr And The "Real" Ending
Champion Gundyr is a different version of the Iudex Gundyr boss found only in an optional pathway towards the end of the game. The optional area of the Untended Graves is a re-skinned version of the Cemetery of Ash, the introductory area in Dark Souls 3, which itself is found after the optional area of Oceiros.
After defeating the consumed king, the player can fight Champion Gundyr which leads to the "End of Fire" ending. It also leads to the Coiled Sword fragment, which functions as a reusable Homeward Bone, as well as a few farmable Black Knights.
2 Dark Souls 3: The Old Wolf Of Farron's Stray Demon
In Farron Keep, players who spend some time exploring might find themselves face-to-face with a gargantuan wolf high up in a tower. Beyond the Old Wolf, though, is another stairway and elevator that leads to the secret Stray Demon fight atop the crumbling walls of Lothric.
The Stray Demon is ashen and flameless in appearance as if it has been stranded for countless years. There's a variety of useful items up there, too, and the Stray Demon doesn't trigger a boss wall, making it an easy boss to grind out even at low levels.
1 Dark Souls 3: The Carthus Sandworm
The Carthus Sandworm is the first thing that players see in the Smouldering Lake optional area (if they don't get shot down by monstrous crossbow bolts first). The boss is gigantic, unyielding, and guards the entrance to the Old Demon King boss room.
What many players don't know, though, is that it actually can be defeated. It's weak to magic, dark, fire, and thrusting damage, but it'll take quite a long time to whittle down its massive 6000 health while dodging its impressively destructive attacks.