World of Warcraft recently released its latest expansion, Shadowlands, and the end-game WoW raid bosses are already proving to be exceedingly difficult for even the top guilds. Castle Nathria, for example, threw players for a loop thanks to Shadowlands' more complex boss mechanics – it was only cleared on Mythic difficulty for the first time more than two weeks after the raid was released.

RELATED: Shadowlands: 5 Best DPS Classes (& 5 Worst)

In World of Warcraft's 17-year history, there have been a number of near-unbeatable raid bosses that only fell after several hundred attempts. Bosses like Kel'Thuzad, Kael'Thas, and C'Thun are each worth an honorable mention as they took many months to be cleared back in the early days of World of Warcraft. 

Sadly, not many guilds kept track of how many attempts were made on these bosses. Luckily, guilds in later expansions started tallying attempts, making the process for finding the hardest raid bosses of all time far easier.

Updated July 19, 2021 by Erik Petrovich: The bosses of World of Warcraft's history are figurative titans, capable of bringing down the most coordinated and careful guilds most of the time on release. While Shadowlands has now introduced two major raids (Castle Nathria and the Sanctum of Domination) neither Sire Denathrius nor Sylvanas Windrunner has ranked among the Top 10 most difficult World of Warcraft raid bosses – although plenty of guilds are still vying for the World First mythic completion of the latter.

10 Blackhand, in the Blackrock Foundry

• Expansion: Warlords of Draenor
• Number of Attempts: 325

Blackhand was the final boss of Blackrock Foundry in the Warlords of Draenor expansion. Blackhand's first phase usually went easy enough, with a few distractions thrown at players with the Marked for Death debuff for example. When Blackhand fell to 70% health, his second phase would begin along with a transitionary explosion, and then every 50 seconds he would summon a Siegemaker to the fight.

It was a raid that required intense communication and focus, as well as knowing exactly what to do at any given moment. It's no wonder it took 700 attempts for the world's second Blackhand kill.

9 Jaina Proudmoore, in the Battle for Dazar'Alor

• Expansion: Battle for Azeroth
• Number of Attempts: 346

Jaine Proudmoore was a boss in Battle for Azeroth's raid Battle of Dazar'Alor. Her fight was not particularly difficult for any laundry list of reasons like Blackhand, but rather because of one mechanic unique to Jaina: the Chilling Touch debuff.

RELATED: World of Warcraft in 2020: 5 Classes To Try Next (& 5 TO Skip)

Chilling Touch slowed players by 2 percent, stacked, and when it reached full stacks froze the player solid. One guild went to the extreme measure of changing the race of every member of the raid to troll, as trolls had a racial passive that reduced movement impairing effects.

8 Queen Azshara, in the Eternal Palace

• Expansion: Battle for Azeroth
• Number of Attempts: 359

Queen Azshara was a boss in Battle for Azeroth's The Eternal Palace raid. Queen Azshara was a legendary character in World of Warcraft going all the way back to Cataclysm, and her raid was just as legendary for its, to put it lightly, unique raid mechanics.

Most of her skills revolved around targeting players who were in her line of sight. A successful Azshara raid required constant movement and constant knowledge of what was around the player – for casters, this was nigh on impossible.

7 Fallen Avatar, Penultimate Boss of the Tomb of Sargeras

• Expansion: Legion
• Number of Attempts: 453

The Fallen Avatar is one of the few bosses listed here that was not the final boss of the raid. As the second to last boss of The Tomb of Sargeras in Legion, the Fallen Avatar raid was full of random elements that made consistent progress on the boss extremely difficult.

One such ability was Dark Mark, a debuff with unlimited range that targeted three random raid members, dealt massive damage, then launched them into the air. He also dealt an insane amount of damage in waves to players close by based on buffs the boss gained constantly. The only way to get a good run with the Fallen Avatar was to hope party members with low health didn't get targeted.

6 Archimonde, in Hellfire Citadel 2.0

• Expansion: Warlords of Draenor
• Number of Attempts: 472 Attempts

Archimonde was the final boss of the Warlords of Draenor raid Hellfire Citadel, a callback to the dungeon of the same name from The Burning Crusade. Archimonde's fight required players to constantly be aware of each other and constantly communicate positioning, as well as random elements that turned the boss fight into a roll of the dice most of the time.

One such random element was the Doomfire spell, a spirit cast by Archimonde that dealt a massive amount of damage to a player for 10 seconds before switching to a new player. The spirit was tough to kill alongside Archimonde, and some raids turned all of their attention to the spirit once it spawned.

5 Yogg-Saron, Old God of Ulduar

• Expansion: Wrath of the Lich King
• Number of Attempts: 500+

Yogg-Saron is an Old God in World of Warcraft, near-omnipotent ancient beings that envelop and consume worlds across the universe. While the version players fought in Ulduar in Wrath of the Lich King used a fraction of its true power, it nonetheless proved tough – especially on its hardest difficulty.

RELATED: Warcraft: 10 Most Powerful NPCs From The Lore

The raid was designed for keepers, NPCs that could be summoned during the raid, to also aid raids in defeating the Old God. For maximum difficulty, some guilds ignored these keepers, choosing to take on Yogg-Saron without this help designed for the raid.

4 Ragnaros 2.0, in The Firelands

• Expansion: Cataclysm
• Number of Attempts: 500+

Ragnaros was a boss in Vanilla World of Warcraft who received a revival in Cataclysm's Firelands raid. It was not a particularly tough fight for any unfair or broken mechanics (although it certainly wasn't a walk in the park). It was tough because it took most guilds more than 20 minutes to complete, though it wasn't one of the hardest raid bosses in WoW.

20 minutes is a long time for mistakes to happen, and even one or two party members' deaths could jeopardize the fight in the long run. Focusing for a third of an hour on pinpoint precision and timing is tiring – it's no surprise many guilds simply stopped keeping track of attempts out of tedium.

3 Garrosh, in The Siege of Orgrimmar

• Expansion: Mists of Pandaria
• Number of Attempts: 638

Garrosh holds a unique spot on this list as one of the few bosses who can claim a massive number of attempts in the 10-man raid category. In Mists of Pandaria 10-man raids and 25-man raids dropped the same loot, and while his fight was not particularly difficult due to one mechanic – like Ragnaros it just went on for absolute ages.

Players had to be on-point and exactly correct with their timings if they wanted to down Garrosh, and that's quite hard to do over an average of 15 minutes.

2 Kil'Jaeden, Final Boss of the Tomb of Sargeras

• Expansion: Legion
• Number of Attempts: 654

Kil'Jaeden was the final boss of Legion's Tomb of Sargeras, following the Fallen Avatar fight. Upon release, the Kil'Jaeden fight was actually bugged, so much so that some guilds stopped running the boss altogether until a fix came out. Kil'Jaeden's abilities also did far too much damage for healers to mitigate, almost as if the developers wanted to design a raid that was functionally impossible.

Eventually, Kil'Jaeden fell, and after a round of debuffs more than a few guilds got in on the action. But at 654 attempts, Kil'Jaeden lived up to his title as the Supreme Commander of the Burning Legion and put up quite a fight to match, solidifying him as one of the most iconic WoW bosses.

1 Uu'nat, The Near-Undefeatable Finale to the Crucible of Storms

• Expansion: Battle for Azeroth
• Number of Attempts: 731

Uu'Nat in Battle for Azeroth's Crucible of Storms is the unquestioned hardest boss in WoW history as the most attempted raid boss the game, and it's because of one mechanic. Unstable Resonance was an ability that affected more than half of the raid at once, and forced players to avoid teammates who had a different resonance type from them. If players touched and had different debuffs, the ability would trigger and deal a lethal explosion within 10 yards of the players.

It was the hardest WoW boss at the time and one that required a lot of patience to overcome. Eventually, it was completed, but not without a complaint from the World of Warcraft community on the design of the Mythic difficulty mechanics.

NEXT: World of Warcraft: Should You Play Classic Or Shadowlands?