Demon's Souls players can progress through each Archstone in whatever order they want, but the Archstone of the Small King is the exception. After beating the Tower Knight in world 1-2, players must first attain an Archdemon's Soul before moving on to world 1-3. Another thing that sets this Archstone apart from others is that there are four bosses rather than three, and their difficulty varies widely. When determining which of these four bosses is the hardest, it's vital to look at each boss' intrinsic difficulty, but in this case, the player's progress plays a huge role.
Bosses are one of the main allures of Demon's Souls and the Souls franchise as a whole. The concept of battling a massive knight with a tower shield or a huge demon is really tempting for some players, and is what much of the franchise's success hinges on. As the predecessor to Dark Souls, it's clear that Demon's Souls was still figuring some things out, but it manages to stick the landing 90% of the time with the way it implements its boss battles. The Archstone of the Small King may be the first one, but that doesn't mean it's the easiest by any means.
Gates of Boletaria - Phalanx
On its own, the Phalanx isn't a difficult boss, but there's a few limiting factors that make this fight much more formidable. For starters, this is the only fight in the game that players are required to do in Soul Form, meaning their health will be stuck at 50% of its maximum capacity (75% with the Cling Ring). Additionally, players have yet to unlock the ability to level up their characters and spend souls at this point, meaning they'll have to make do with whatever their starting stats were. Even in terms of equipment there aren't many options for diversification at this point.
On the bright side, Phalanx is predictably weak to fire, starting a trend among many of the game's boss battles. While players don't have the spells or enchanted weaponry to exploit that weakness yet, the level leading up to it gives them more than enough firebombs and pine resin, both of which make this fight much easier to handle. For players that aren't able to piece together the Phalanx's weakness, it can be serious threat, but once this key information is learned the fight is trivialized. The boss arena is also super forgiving, featuring pillars that players can easily use as cover to heal up.
Boletarian Palace - Tower Knight
In truth, the Tower Knight is more intimidating than it is dangerous. Its massive stature will surely make players feel helpless against it, and the barrage of archers set up along the perimeter of the arena also pose a huge threat. Naturally, taking these archers out should be the first priority of players, and then it's time to figure out how to take down the Tower Knight. A few swipes at the giant's ankles will reveal a glaring weakness, and it shouldn't be too hard for players to capitalize on this.
In terms of difficulty, the Tower Knight is able to deal heavy damage to players and is practically invincible from frontal assaults thanks to its shield. The area of effect on its many attacks can prove difficult to deal with at first, but don't deal too much damage overall. As long as players manage to stay behind the Tower Knight and take out the archers before getting started, they should have an easy enough time with him. At this point, players are required to obtain an Archdemon's Soul before continuing, so they should be much more powerful before the next boss.
Inner Ward - Penetrator
Players will probably be tempted to return to the first Archstone after getting their first Archdemon's Soul, but that might not be a good idea. Though it's entirely possible to defeat the Penetrator this early, it's a huge challenge. This boss doesn't have any gimmicks that will make him easier to defeat, making it a pure test of combat skill on the part of the player. His attacks deal damage through shields, so melee builds will want to be extra careful about that, and his long reach and sweeping strikes are difficult to dodge.
The sheer amount of damage this boss can put out is insane, and his moves can be very difficult to read at first. To make matters worse, he has an ability where his weapon glows with cursed energy similar to the Cursed Weapon magic spell and he impales the player. This will almost always result in an instant kill, so it's best avoided. It shouldn't be hard to tell that the Penetrator is much harder than either of the bosses that came before him, but whether or not he is tougher than the following boss is a point of debate among the community.
The King's Tower - Old King Allant
The final boss of Demon's Souls awaits players at the top of the King's Tower, and it will push players to the limits of their abilities. Old King Allant wields the Soulbrandt and a form of demonic magic that allows him to move at incredible speeds. If players aren't caught off guard by his blindingly quick strikes, they may instead fall victim to his massive AoE attacks. Even worse, one of his moves, Soul Sucker, drains a level out of the player's highest stat, meaning this fight can get more and more difficult with each attempt.
Players will need to be extra vigilant during this fight and have quick reaction time in order to come out alive, and like the Penetrator before him, there's no gimmick mechanic to make this easier. Many of Demon's Souls' bosses have a fatal weakness that players can exploit, but that isn't the case for Old King Allant. Since this is likely the last boss that players will face off against, they should be adequately leveled for the encounter, but even that isn't always enough to ensure victory.
Demon's Souls - Archstone of the Small King Hardest Boss
Ultimately, competition is tight between the Penetrator boss and Old King Allant. Phalanx and Tower Knight aren't easy by any means, especially for new players to the franchise, but these two bosses blow them out of the water in terms of difficulty. Overall, Old King Allant is the more difficult of the two, as he features a wide array of both physical and magical attacks that can easily catch players off guard. His Soul Sucker ability is also a huge detriment to some players, making him one of the only bosses with the ability to permanently damage the player. As the final boss of Demon's Souls, it's fitting that he'd be the most difficult boss of the Archstone.
Demon's Souls is available now on PS5.