Demon's Souls is a game well-known for its challenging boss fights, treacherous terrain, and sometimes down right unfair traps that make the game difficult. The crazy part about this is that all that wasn't enough for some fans of the series, who opted for a bit more of a challenging experience.
Fan challenges are a common staple of the Soulsborne franchise, because simlpy beating the games has become more normalized as the games gained popularity. Fans have beaten Dark Souls with nothing but Donkey Kong bongo controllers, and Bloodborne using only their sidearms. Demon's Souls is no different when it comes to the extremity of its fan challenges.

No Damage Run

The no damage run is a classic challenge run for the Soulsborne games. It's so classic, that Dark Souls 2 even had a ring that you could only obtain by completing the game without taking damage. Since Demon's Souls is already a ten year old game, fans were quick to jump into the remake and complete the same run, without much difficulty.
Funnily enough, a no damage run is actually considered an entry level challenge for demon's souls since players have had so much time to learn the patterns of the game and its enemies. The remake hardly changed anything aside from updating the graphics so, a no-hit run is still pretty standard in 2021. These challenges served as a jumping off point for the truly crazy challenges fans are coming up with now.

Soul Level 1 Challenge

Post Parry in Demons Souls
Another classic challenge run of Demon's Souls is to complete the game without leveling up. Demon's Souls allows players to raise their soul level by upgrading their stats, which helps with defeating tougher enemies. Players can up their attack, as well as HP and defense to tank more hits. The point of this challenge is to keep their level the same as it is at the very start of the game.
Being soul level 1 comes with a lot of subtle challenges aside from low stats. Having lower stats means that certain armor sets and weapons are unavailable to the player. This means they'd have to use weaker items throughout the game, unable to boost their damage potential through normal means.

Fractured Mode

Fighting the Flamelurker in Demon's Souls Remake
Fractured mode is a new feature introduced in the remake of Demon's Souls. In this mode, the world is reversed, as well as the player character. This isn't too much of a challenge because nothing much changes aside from the world itself but it can definitely throw a lot of veteran players off because things seem to be in completely different places since directions are reversed.
The biggest challenge of fractured mode is that the player character is reversed but the controls stay the same. This means that attacks on the left side still come out with a press of R1, which makes it feel like playing the game reflected off a mirror.

Sorcery Only Challenge

Sorcery attack in Demon's Souls
This challenge sums itself up pretty nicely in the name. With this challenge, players can only use sorceries which has its own hidden challenges within. For starters, this means players have to manage their MP extremely well so they don't run out and become unable to perform spells. On top of managing their meter, they have to manage item use because they have a limited amount of items to replenish MP.
These runs get easier with time as the character build has more options and more powerful sorceries become available. The toughest part is definitely the beginning when MP is low and has to be restored constantly, but offensive items like firebombs and buffs can supplement that early on as well.

Permadeath

Looking at the Demon's Souls tutorial zone
What if Demon's Souls played like an old arcade game where you only get one life and then have to start over from the beginning? That's exactly how the permadeath challenge plays and it's a bit more approachable than a no-hit run. This run is one of the first that fans get into when they start challenge runs because it doesn't require an insane amount of knowledge about the game like others do.
This challenge is still very difficult despite its accessibility, but it's still fun to try out once players have beaten the game once or twice. The most difficult part of this challenge is defeating the Vanguard Demon at the beginning. It's an optional part of the challenge that can be considered a tutorial outside of the main game, so don't stress about it too much.

Guts Mode

Guts mode character waving in Demon's Souls
Many enemies, levels, and weapons take inspiration from the iconic manga series Berserk in Soulsborne games. Fans have created a bunch of criteria for a challenge run, where the character resembles Guts, the protagonist of Berserk.
To complete this run, players can't use magic, they can only use the bastard sworn until they get the Dragon Bone Smasher in 2-3, and they can only wear the Gloom Armor. The only stats players can upgrade as Guts are strength, endurance, and vitality and they must start as a barbarian class.

The Pugilist Run

Showcasing the Hands of God weapons
In Demon's Souls, players are able to attack without weapons equipped, using their bare fists. In the remake, there are even specific backstab and parry animations for weaponless attacks, and they look great.
The pugilist challenge is completing the game using nothing but the fists of the character. There're certain ways to make it easier like using fist weapons including Claws or the Hands of God. Fist weapons aren't that great so it can be difficult to do high damage, and they're also not available until a decent amount into the game. Until a good fist weapon is found, players will have to use their wits to make up for the lack of damage.

No Shields

Fools Idol fight in Demon's Souls
Shields are just as useful in the souls series as the weapons available to the player. They can be the difference between life and death in so many occasions, and get players out of sticky situations. The no shield run is one that takes a lot of getting used to because blocking is such an essential mechanic in Demon's Souls.
Without the ability to block, players must have extensive knowledge of enemy attack patterns, and awareness of where they can attack in order to evade attacks without having to block. That being said, just because shields aren't available, doesn't mean blocking is impossible. Some weapons like greatswords allow players to block while two-handing the weapon. Also, replacing a shield with another weapon in that hand opens up new options for combos and higher damage, so it isn't as restricting as it might sound.

Hitless

Fighting Dragon God in Demon's Souls
This challenge is worlds different from the no damage run because a no damage run means players can block. In the hitless run, blocking an attack is considered failing because it made contact with the player, one way or another.
This run is essentially a combination of the no damage run and the no shields run because there's no getting hit and no blocking. All players can do to avoid damage here is roll and space themselves well out of the way of incoming attacks.

Soul Level 0

Fighting in the Boletarian palace in Demons Souls
It isn't technically possible to get soul level 0 in Demon's Souls but fans have found ways around that by using save editors. To reach soul level 0, players must set all their stats to 0 which can turn the entire experience of the game upside down.
Certain weapons only show their true potential in this mode because of how most weapons scale with a character's stats so the game itself plays like a whole new one. Fans have found that offensive items are a lifesaver in this run, so it's important to stock up on everything before going anywhere.