History ThatOneBoss / RuneScape

* Vanstrom Klause returns in Sins of the Father, and is somehow even worse than his previous incarnation. First off, in The Branches of Darkmeyer, you got a blisterwood weapon for each combat style, but in Sins of the Father, you're stuck with the Blisterwood Flail, which is a terrible melee weapon. Vanstrom has 750HP, a considerable Defence level, and attacks with powerful magic that can drain your Attack level or leech health on hits. He's also got three special attacks; he can summon a blood orb to power up his magic, summon an acidic bloodveld that has to be killed at range (you ''did'' bring a stack of darts set to long-ranged, right?), and can use the darkness attack from The Branches of Darkmeyer (thankfully, you no longer need to angle the camera away from him). Finally, when you drain him to 0 HP, he pulls a Nomad, recovering 200 health and hammering you with powerful typeless magic, while also summoning lightning bolts to strike throughout the arena every other second.

* Vanstrom Klause returns in Sins of the Father, and is somehow even worse than his previous incarnation. First off, in The Branches of Darkmeyer, you got a blisterwood weapon for each combat style, but in Sins of the Father, you're stuck with the Blisterwood Flail, which is a terrible melee weapon. Vanstrom has 750HP, a considerable Defence level, and attacks with powerful magic that can drain your Attack level or leech health on hits. He's also got three special attacks; he can summon a blood orb to power up his magic, summon an acidic bloodveld that has to be killed at range (you ''did'' bring a stack of darts set to long-ranged, right?), and can use the darkness attack from The Branches of Darkmeyer (thankfully, you no longer need to angle the camera away from him). Finally, when you take down his health, he pulls a Nomad, recovering 200 health and hammering you with powerful typeless magic, while also summoning lightning bolts to strike throughout the arena every other second.

* Vanstrom Klause returns in Sins of the Father, and is somehow even worse than his previous incarnation. First off, you're stuck with the Blisterwood Flail, which is a terrible melee weapon. Vanstrom has 750HP, a considerable Defence level, and attacks with powerful magic that can drain your Attack level or leech health on hits. He's also got three special attacks; he can summon a blood orb to power up his magic, summon an acidic bloodveld that has to be killed at range (you ''did'' bring a stack of darts set to long-ranged, right), and can use the darkness attack from The Branches of Darkmeyer (thankfully, you no longer need to angle the camera away from him). Finally, when you take down his health, he pulls a Nomad, recovering 200 health and hammering you with powerful typeless magic, while also summoning lightning bolts to strike throughout the arena every other second.

* While the Desert Treasure bosses have mostly been defanged by power creep, in ''Old School'', they're still a very tough fight, especially if you do the quest at a lower level. While Fareed, Dessous, and Damis are fairly manageable as long as you account for their gimmicks, Kamil is an absolute beast. First, he's located on the Ice Path near the God Wars Dungeon, so your stats will be drained periodically, and you can't run or use special attacks. To get to him, you have to wade through hordes of ice trolls and ice wolves, which will hit for 10+ damage frequently id you don't turn on Protect from Melee. When you actually do get to Kamil, as you'd expect, he starts spamming ice spells at you, which always hit for 5 damage, freeze you in place, and interrupt your attacks. Getting into melee range makes it easier, but good luck getting more than a few steps towards him at a time before getting frozen again - and you've still got the stat drains from the blizzard to contend witb.

** In phase 4, Araxxor is replaced by Araxxi, whose normal attacks are stronger than Araxxor's and she is able to switch rapidly between magic and ranged attacks depending on which one you are praying against, so to take less damage you have to flip between prayers. She can use several of Araxxor's special attacks too, and when she is is down to 1/4 of her health she stops using special attacks and launches a [[PinballProjectile projectile that bounces around the arena]] for the rest of the fight and homes in on you every few bounces, dealing a huge amount of damage very fast until you move and it continues bouncing. And you have to kill Araxxi as quickly as possible because her enrage meter increases with every attack, increasing her damage. And on top of all those complicated mechanics, you are only allowed to fight Araxxor alone or with a single other player and you cannot teleport out of Araxxor's lair, so once you start the battle the only way out is to die or to win. Because of how crazy complicated Araxxor's fight is, [[GuideDangIt you really should spend a long time studying a guide on how to fight him before you attempt it.]]

* "Dream Mentor" has you fight a boss that has ''everything'' designed to make it difficult and frustrating. While [=RS3=] has it easier due to adrenaline and power creep, [=RS2=] and OSRS have it be an incredibly painful fight. This boss takes place in an instance (which, in OSRS, means your unprotected gear ''vanishes permanently'' if you die) and has the following problems: prayers are disabled (including the protect item prayer, which makes it being in an instance even worse), it can't be safespotted, has stupidly high melee and ranged defence, uses ranged attacks if you're more than one tile away from it, hits very hard and very often, summons mooks that also hit hard and often and respawn if you kill them, doesn't allow you to walk under it, doesn't allow you to teleport out unless you use the altar far away from it in the room, and is the ''first phase'' of a four phase fight. The only upsides are that it's so vulnerable to magic that you can reliably hit it even in full melee armour, and that the other three phases are so easy that even when (not if, when) it cleans your entire inventory of most of your food, you won't have much trouble doing the rest. Knowing about the former is also unlikely, as the number of times you can use magic reliably in melee armour can be counted on one hand, and you're probably on the Lunar spellbook because of where the quest takes place on anyway, but it's an option nonetheless. Dream Mentor was initially released as an experienced quest, but was later changed to master because of how hard this one phase is.

* The original ThatOneBoss of [=RuneScape=] is the [=TzTok-Jad=], the boss of the Fight Cave minigame. The [=TzTok=]-Jad does not have any special attacks, but he doesn't need any, because his normal attacks deal thousands of points of damage with every hit. His attacks can be completely blocked with prayer and his magic and ranged attacks have a delay so you can switch prayers before they hit, but failing to block as little as two attacks will likely result in your death and having to start the Fight Cave all over. And when he is at half health, he summons four [[MookMedic Yt-HurKots]] to restore his health, and if you fail to stop them from healing him back to full health, they will appear again the next time he gets to half health. Plus, you must fight him alone, without the help of familiars or other players. [=TzTok=]-Jad was the most powerful enemy in the game before the [[EldritchAbomination Corporeal Beast]], which was designed to not be beatable by a single player until more powerful items were later added. And if the Fight Cave and [=TzTok=]-Jad are not hard enough for the player, the Fight Cave now has a sequel called the Fight Kiln where the player has to fight through waves of even harder enemies, including a total of seven stronger versions of the [=TzTok=]-Jad called [[BossInMookClothing TokHaar-Jads]], which do not summon healers but have even more ridiculously high damaging attacks, enough to possibly kill you in one hit, and the last two [=TokHaar=]-Jads appear at the same time, which probably would be impossible to beat if the arena didn't have a safe spot where you can hide from one of them while fighting the other. After beating all those [=TokHaar=]-Jads, the actual boss of the Fight Kiln, Har-Aken, doesn't seam so bad.

** Yk'Lagor the Thunderous was this with his one-hitting earthquake attack before the players figured something out.

** Shadow-forger [[TheUnpronounceable Ihlakhizan]]. Hits up to over 80% of maximum health with his special attack, which also drains all your stats to half. Even if you tanked it, you probably won't stand a chance after that. This is devastating to freeplayers, who have no method of recovering lost stats. Members can at least make a potion to recover. Although this special attack is very easy to dodge if you know how to. Just like the fight with Yk'Lagor, you have to get behind the pillars in the room when he preparing to use the attack.

** Kal'Ger The Warmonger, the last boss of Daemonheim, only found on the last three floors, is also a huge challenge. Kal'Ger is a MarathonBoss who goes through six phases as his hit points are worn down, starting unarmed and then switching between 5 weapons. He is able to drain prayer and if the player uses protections prayers for too long he will do a special attack that can deal over 8000 damage. During the bow phase, he drains your defense with every attack, and during the final phase where he wields a maul, his attacks get faster and if the player uses the turmoil prayer he will copy it to greatly boost his own stats. And if you try hiding from him during any of the phases where he uses melee weapons he will send you into a lava pit.
* Tok Haar Hok from the Elder Kiln was a big one. Hok is essentially a lava monster who acts as a prophet for an Elder God of fire, and he lives up to that big time. Hok himself isn't terribly tough, but once his health hits halfway, he'll try to heal. To prevent this, you must stun him before he steps into the lava waterfall. Easy enough. Did we mention that this is in a tiny arena, he spawns heavy hitting minions, and the floor of the arena also erupts lava from time to time, forcing you to be on the move? To make matters worse, The Elder Kiln quest was the first major combat quest released after the overhaul to combat, so many players had not yet mastered the new system.

* True to their name, the Elite Dungeons have some very difficult boss encounters to complement the [[DemonicSpiders already tough mobs]].

** Nomad in his sequel quest. In the sequel, his attacks are even more powerful than they were before and he now has an artificial god under his control that you have to occasionally dodge attacks from.

* "Dream Mentor" has you fight a boss that has ''everything'' designed to make it difficult and frustrating. While [=RS3=] has it easier due to adrenaline and power creep, [=RS2=] and OSRS have it be an incredibly painful fight. This boss takes place in an instance (meaning your gear is unobtainable if you die) and has the following problems: prayers are disabled (including the protect item prayer, which makes it being in an instance even worse), it can't be safespotted, has stupidly high melee and ranged defence, uses magic attacks if you're more than one tile away from it, hits very hard and very often, summons mooks that also hit hard and often and respawn if you kill them, doesn't allow you to walk under it, doesn't allow you to teleport out unless you use the altar far away from it in the room, and is the ''first phase'' of a four phase fight. The only upsides are that it's so vulnerable to magic that you can reliably hit it even in full melee armour, and that the other three phases are so easy that even when (not if, when) it cleans your entire inventory of most of your food, you won't have much trouble doing the rest. Knowing about the former is also unlikely, as the number of times you can use magic reliably in melee armour can be counted on one hand, and you're probably on the Lunar spellbook because of where the quest takes place on anyway, but it's an option nonetheless. Dream Mentor was initially released as an experienced quest, but was later changed to master because of how hard this one phase is.

* The six Legiones found in the Monastery of Ascension are also frustrating to fight. [[GlassCannon Although they have relatively low health and don't take long to kill, their special attacks are absolutely devastating and can kill you in seconds if you don't constantly dodge them.]] Plus, in order to fight any of them, you have to obtain a keystone, which can only be dropped randomly from the other monsters in the dungeon or purchased from another player, but each keystone only allows you to attempt to fight a Legione exactly once. So if you die while fighting a Legione you will have wasted the keystone and will have to get another. The game actually gives you an Achievement for killing each of the Legiones without moving, forcing you to tank all of the massive damage from their attacks. This can be ThatOneAchievement unless you choose to use the extremely expensive and rare Deathtouched Dart to kill them.

* The final boss of "Heroes' Welcome", Tarshak, aka "Abomination", is obnoxious. The first phase of the fight is easy, if annoying, as while most of his attacks are obviously telegraphed, the player needs to guide a [[SuperPersistentMissile inexplicably homing fireball]] towards pillars after weakening them with a pickaxe, with the catch that the projectile has to hit the player (instead relying on SplashDamage to bring the pillar down), requiring the player to eat a powerful unblockable attack per pillar that does a considerable amount of fast-attacking damage-over-time until they run into a fountain to put out the flame. The sting in the tail comes in the form of the fight's second and final phase, where the player has to bait the now limping Abomination under randomly spawning area-of-effect falling rocks to whittle down his health (as he's invulnerable to direct attacks until he's near death), usually requiring the player to take rapid damage as the rocks often spawn too close to the walls of the arena to simply stand on the other side. Making matters worse, the Abomination continues spewing homing fireballs, with the damage over time replaced with leaving behind a lingering area-of-effect trap at the point of impact. This wouldn't be a major problem, if not for the fact that the Abomination also has a dash attack that is poorly telegraphed, does considerable damage and stuns the player on hit for a prolonged period while putting him within range to use his fast, accurate, and powerful melee attacks. If the player happens to be under either one, or worse, both types of area of effect traps when the stun takes effect (which can happen with no warning, as rock locations spawn randomly without warning and the Abomination can launch fireballs while in the middle of the dash attack), they're pretty much screwed unless they've got lots of health.

* The final boss of "Heroes' Welcome", Tarshak, aka "Abomination", is obnoxious. The first phase of the fight is easy, if annoying, as while most of his attacks are obviously telegraphed, the player needs to guide a [[SuperPersistentMissile inexplicably homing fireball]] towards pillars after weakening them with a pickaxe, with the catch that the projectile has to hit the player (instead relying on SplashDamage to bring the pillar down), requiring the player to eat a powerful unblockable attack per pillar that does a considerable amount of fast-attacking damage-over-time until they run into a fountain to put out the flame. The sting in the tail is the fight's second and final phase, where the player has to bait the now limping Abomination under randomly spawning area-of-effect falling rocks to whittle down his health (as he's invulnerable to direct attacks until he's near death), usually requiring the player to take rapid damage as the rocks often spawn too close to the walls of the arena to simply stand on the other side. Making matters worse, the Abomination continues spewing homing fireballs, with the damage over time replaced with leaving behind a lingering area-of-effect trap at the point of impact. This wouldn't be a major problem, if not for the fact that the Abomination also has a dash attack that is poorly telegraphed, does considerable damage and stuns the player on hit for a prolonged period while getting in some decently powerful melee hits of his own. If the player happens to be under one, or both types of area of effect traps when the stun takes effect (which can happen with no warning, as rock locations spawn randomly without warning and the Abomination can launch fireballs while in the middle of the dash attack), they're pretty much screwed unless they've got lots of health.

** The Pharaoh, the FinalBoss of the Menaphos arc, is an absolutely miserable fight. Not only is he [[DamageSpongeBoss tankier than many raid bosses]] despite being a DuelBoss, not only is only one of his attacks not a FixedDamageAttack, and not only is he a massive DifficultySpike as most of the arc has very little combat, but each of his three special attacks (which he uses after every third-auto attack) qualifies as a ThatOneAttack:
*** His Corrupted Fire attack is an area-of-effect trap that does a fixed, unmissable 1000 damage per tick, making him capable of wiping out even the highest level characters in seconds.
*** His stun attack does large amounts of unmissable damage per tick which increases rapidly (starting at 100 damage and increasing by an additional 100 per tick to a maximum total of 5500 damage) that can only be countered with specific moves in Evolution of Combat/Revolution mode (which have a lengthy cooldown) and has virtually no counter in Legacy mode (making the fight effectively {{Unwinnable}} in Legacy).
*** His "wrath of the gods" attack does massive amounts of instantaneous nuke damage, dealing anywhere from 3000-6000 damage at a moment's notice. While this is the only attack that doesn't deal fixed damage (and as such can be reduced by the Protect from Magic prayer), it's also the only attack that can't be mitigated by fast reflexes.
*** Last, but by no means least, he TurnsRed once he's reduced to half health, giving him an area-of-effect wall of fire to dissuade melee users and cranking up his damage even further, making it incredibly likely that his "wrath of the gods" attack will be a OneHitKill regardless of health.

* The final boss of "Heroes' Welcome", Tarshak, aka "Abomination", is obnoxious. The first phase of the fight is easy, if annoying, as while most of his attacks are obviously telegraphed, the player needs to guide a [[SuperPersistentMissile inexplicably homing fireball]] towards pillars after weakening them with a pickaxe, with the catch that the projectile has to hit the player (instead relying on SplashDamage to bring the pillar down), requiring the player to eat a powerful unblockable attack per pillar that does a considerable amount of fast-attacking damage-over-time until they run into a fountain to put out the flame. The sting in the tail is the fight's second and final phase, where the player has to bait the now limping Abomination under randomly spawning area-of-effect falling rocks to whittle down his health (as he's invulnerable to direct attacks until he's near death), usually requiring the player to take rapid damage as the rocks often spawn too close to the walls of the arena to simply stand on the other side. Making matters worse, the Abomination continues spewing homing fireballs, with the damage over time replaced with leaving behind a lingering area-of-effect trap at the point of impact. This wouldn't be a major problem, if not for the fact that the Abomination also has a dash attack that is poorly telegraphed, does considerable damage and stuns the player on hit for a prolonged period while getting in some decently powerful melee hits of his own. If the player happens to be under one, or both types of area of effect traps when the stun takes effect, they're pretty much screwed unless they've got lots of health.

* The championship fight with General Graardor in The Mighty Fall, where he picks up a weapon. The match bans prayer and requires you to fight with a kyzaj, which is a sluggish (albeit fairly decent) two-handed weapon. Graardor's basic attacks are fairly manageable, but he has a bunch of special attacks that he spams nonstop. For starters, he creates unblockable, undodgeable shockwaves that take off up to 17% of your max HP, and can only be reduced by staying at the edge of the platform. He also sweeps the kyzaj horizontally, doing ''40%'' of your max HP in damage if you get hit by it. You get next to no time to dodge it, too; if your internet hiccups, or you heal at a bad time, you get a kyzaj to the face. Finally, every time you take off 20% of his mountain of HP, he smashes the platform, causing one of the edges to crumble, hitting you for another 40% of your HP if you get hit by it, and reducing the area to stand in.

** The final boss, Seiryuu the Azure Serpent, is an unholy combination of MarathonBoss and [[HealingFactor DPS race]] in draconic form. His normal magic attacks deal little damage, and his breath can be easily predicted and defended against, those are not the main difficulty factor. The real threat are the waves of shadow hands he constantly summons throughout the battle. If you get caught in them, they inflict so much rapid typless damage that it's more or less instant death, meaning even a single mistake in your movement will end the attempt. Then comes the issue of actually HURTING him. To win, you have to destroy three crystals on his collar, which are only made vulnerable when you inflict ''800k'' damage on Seiryuu himself. The crystals themselves have between 150k to 250k HP depending on group size, and you need to destroy them ''fast'' because not long after Seiryuu is stunned, shadow creatures appear at the other end of the arena, and if they reach Seiryuu, they will heal the crystals for over 30k each, [[AllForNothing undoing all of your hard work]]. In a team, one person can stay behind and kill the creatures before they reach, but if you're soloing you will need ''crazy'' dps to destroy even one crystal before the healers reach it. And once Seiryuu recovers, you have to DPS him down ''again'' to expose the crystals. All of these factors make Seiryuu a horribly protracted boss fight where even one slip-up can result in a failed battle and broken keyboards.

** The second boss of the Temple of Aminishi, Masuta the Ascended, is without doubt a nightmare. His first phase has him launching incredibly powerful attacks with all 3 styles, and sometimes summoning clones to deal extra hits. His special attacks are no joke either. He will do a melee spinning attack that lasts ''15 seconds'' and will inflict massive damage on anyone in range not using defensive abilities. His other special is a powerful magic barrage that can be dodged, but it is rather difficult to tell where the blasts are going to land. In the second phase, he becomes invincible and summons a multitude of water monsters to attack you. These monsters attack very fast, have incredibly long range, and if you do not kill them from close range, you miss out on a defensive buff that is vital to the final phase. After he has summoned enough, he enters the third phase, where he alternates between ranged and a power magic attack that can easily kill you if you didn't get enough buff stacks in the second phase. Oh, and any of the water monsters that you didn't reach in phase 2 will still be shooting at you, pressuring your limited supplies even more.
** The final boss, Seiryuu the Azure Serpent, is an unholy combination of MarathonBoss and [[HealingFactor DPS race]] in draconic form. His normal magic attacks deal little damage, and his breath can be easily predicted and defended against, those are not the main difficulty factor. The real threat are the waves of shadow hands he constantly summons throughout the battle. If you get caught in them, they inflict so much rapid typless damage that its more or less instant death, meaning even a single mistake in your movement will end the attempt. Then comes the issue of actually HURTING him. To win, you have to destroy three crystals on his collar, which are only made vulnerable when you inflict ''800k'' damage on Seiryuu himself. The crystals themselves have between 150k to 250k HP depending on group size, and you need to destroy them ''fast'' because not long after Seiryuu is stunned, shadow creatures appear at the other end of the arena, and if they reach Seiryuu, they will heal the crystals for over 30k each, [[AllForNothing undoing all of your hard work]]. In a team, one person can stay behind and kill the creatures before they reach, but if you're soloing you will need ''crazy'' dps to destroy even one crystal before the healers reach it. And once Seiryuu recovers, you have to DPS him down ''again'' to expose the crystals. All of these factors make Seiryuu a horribly protracted boss fight where even one slip-up can result in a failed battle and broken keyboards.

* The six Legiones found in the Monastery of Ascension are also frustrating to fight. [[GlassCannon Although they have relatively low health and don't take long to kill, their special attacks are absolutely devastating and can kill you in seconds if you don't constantly dodge them.]] Plus, in order to fight any of them, you have to obtain a keystone, which can only be dropped randomly from the other monsters in the dungeon or purchased from another player, but each keystone only allows you to attempt to fight a Legione exactly once. So if you die while fighting a Legione you will have wasted the keystone and will have to get another.
** The game actually gives you an Achievement for killing each of the Legiones without moving, forcing you to tank all of the massive damage from their attacks. This can be ThatOneAchievement unless you choose to use extremely expensive and rare Deathtouched Dart to kill them.

** The first boss of the Dragonkin Laboratory, Astellarn the First Celestial, is easily the worst one. She starts fairly tame with her high damaging breath attack...until her mechanics kick in. Her first special is to summon a pulsar star, which has 20k HP and periodically hits all players in the room with high cannonball-type damage, which cannot be reduced with prayer. Her next move is to summon a black hole under a specific player, which deals very high damage to anyone standing on it, and from this point forward she gains massive damage reduction towards all attacks unless players correctly handle the upcoming mechanic. Said mechanic is when Astellarn summons a neutron star for each player, which slowly follows them and hits them for 5k damage if it reaches them. The objective is to lead a neutron star to the black hole, which turns it into a white hole that you must stand in to deal full damage to Astellarn. If you mess up and get hit by the neutron, you're left without a way to effectively damage the boss until the next mechanic rotation, and even if you do create a white hole, there is ''another'' mechanic to deal with. Astellarn periodically summons an energy rain to one quadrant of the arena that moves around throughout the fight. The rain inflicts rapid damage to any players standing in it, and if the rain moves to the quadrant where the white hole is, you have to choose between tanking damage to be able to damage the boss or elongating the fight to save on healing supplies.

*** In the acid path, you have to lure him into an acid pool while dodging spiders that deal enormous damage if they touch you. Failing to drain the acid pool makes makes the 4th phase harder.

*** If the acid path is open, you must lure Highly Acidic Spiders into him if you didn't finish draining the acid pool or didn't take the acid path to prevent phase 4 becomes harder and he will sometimes summon an Acidic Spider that can do enough damage to OneHitKill if it catches you.

** In phase 4, Araxxor is replaced by Araxxi, whose normal attacks are stronger than Araxxor's and she is able to switch rapidly between magic and ranged attacks depending on which one you are praying against, so to take less damage you have to flip between prayers. She can use several of Araxxor's special attacks too, and when she has only 1/4 of her health is left she stops using special attacks and launches a [[PinballProjectile projectile that bounces around the arena]] for the rest of the fight and homes in on you every few bounces, dealing a huge amount of damage very fast until you move and it continues bouncing. And you have to kill Araxxi as quickly as possible because her enrage meter increases with every attack, increasing her damage. And on top of all those complicated mechanics, you are only allowed to fight Araxxor alone or with a single other player and you cannot teleport out of Araxxor's lair, so once you start the battle the only way out is to die or to win. Because of how crazy complicated Araxxor's fight is, [[GuideDangIt you really should spend a long time studying a guide on how to fight him before you attempt it.]]

*** In the acid path, you have to lure him into an acid pool while dodging spiders that deal enormous damage if they touch you.

** In phase 4, Araxxor is replaced by Araxxi, whose normal attacks are stronger than Araxxor's and she is able to switch rapidly between magic and ranged attacks depending on which one you are praying against, so to take less damage you have to flip between prayers. She can use several of Araxxor's special attacks too, and when she has only 1/4 of her health left she uses a special attack that bounces around and does a huge amount of damage very fast if it hits you and you don't immediately move. And you have to kill Araxxi as quickly as possible because her enrage meter increases with every attack, increasing her damage. And on top of all those complicated mechanics, you are only allowed to fight Araxxor alone or with a single other player and you cannot teleport out of Araxxor's lair, so once you start the battle the only way out is to die or to win. Because of how crazy complicated Araxxor's fight is, [[GuideDangIt you really should spend a long time studying a guide on how to fight him before you attempt it.]]

* [[GiantSpider Arraxor]] is one of the hardest and most complicated bosses in the game that can be fought by a single player. The battle takes place in 4 phases. In the first phase, all you have to do is burn down a spider web to allow you to enter one of three paths, which takes about a minute, but it is best to damage him as much as possible before entering one of the paths because any left over lifepoints he has in this phase will heal him in phase 2 or 3. During this he will use several different special attacks, including one attack where he suddenly pulls you toward him and then hits you with thousands of points of damage if you don't get out of the way immediately. In the second phase his behavior is determined by which of the three paths you took, although one of the paths will be inaccessible, and which one it is changes every few days. In the darkness path you have to stay in a narrow beam of light that moves every few seconds to avoid taking rapid damage while Arraxor attacks you from above, and occasionally uses a special attack where you take a huge amount of damage if you are not standing on an egg which may be placed far away from the light beam and every once in a while he will charges at you for massive damages if you don't hit the right button to dodge in a QuickTimeEvent, and failing to dodge makes this path last longer because dodging him is the only way to break the wall to the next phase. In the acid path you have to lure him into an acid pool while dodging spiders that deal enormous damage if they touch you. And in the minion path, which is the hardest path, he summons a large number of spider minions with several different powers, including the very dangerous mirrorback spider which causes you to take any damage you cause to Arraxor as long as it is alive. In phase 3, he uses the special attacks from phase one again but now also uses some of the mechanics from the two paths that were not blocked. In phase 4, Arraxor is replaced by Arraxi, whose normal attacks are stronger than Arraxor's and she is able to switch rapidly between magic and ranged attacks depending on which one you are praying against, so to take less damage you have to flip between prayers. She can use several of Arraxor's special attacks too, and when she has only 1/4 of her health left she uses a special attack that bounces around and does a huge amount of damage very fast if it hits you and you don't immediately move. And you have to kill Arraxi as quickly as possible because her enrage meter increases with every attack, increasing her damage. And on top of all those complicated mechanics, you are only allowed to fight Arraxor alone or with a single other player and you cannot teleport out of Arraxor's lair, so once you start the battle the only way out is to die or to win. Because of how crazy complicated Arraxor's fight is, [[GuideDangIt you really should spend a long time studying a guide on how to fight him before you attempt it.]]
* Another extremely complicated boss that is possible but extremely hard to beat alone is Nex, and even with a group of players she can be a huge challenge. Nex was originally designed to require a group to beat but due to better equipment being added to the game she is now beatable by a single player. Nex has five phases that she goes through as you battle her and has powerful special attacks. In phase one she can spread a virus between the player that rapidly drains stats and she will also sometimes rush across the area and do huge damage to any player she runs into and her magic attacks have a chance of stunning players and disabling their prayers. In phase two she can place shadow traps on the ground and spread darkness that rapidly damages any player too close her and her ranged attacks drain prayer. In phase three she can temporarily make any damage she receives heal her while also summoning blood reavers that can also heal her if they aren't killed quickly and she can mark a player as a sacrifice to deal 10% of their max hitpoints in damage while healing herself 100% of the targets max hitpoint and draining half of all other players prayer if the marked player doesn't quickly get far enough away from her and her regular attacks can hit multiple players at once while also healing her and draining prayer and any ability that cause bleeding damage heals her instead. In phase four she can trap a player in an ice prison that stuns them and deals an emormous amount of damage if they don't either block it or are freed by another player and she can create an ice barrier around herself that deals huge damage to any players close to her and her regular attack drain prayer even more quickly than before and can stun players. During the final phase she doesn't use any special attacks, but she starts by healing 1/6 of her health and her normal attacks become far more powerful and can hit many players at once and she can only be hit with up to 2000 points of damage at a time, and [[KaizoTrap when she finally dies she uses Wrath to inflict damage to any player too close to her.]]

** Although he was made much easier after the release of [[AntiMagic ganodermic]] armour, and later the Evolution of Combat, which made it also possible to block the HPToOne attack by using a shield ability at just the right moment.