Video game easter eggs and hidden locations are nothing new. Since the “dawn of gaming,” developers have been stuffing secrets into their titles. Even early NES games featured special levels and bonus stages. It’s become an “expected” part of the gaming world, to place something hidden within your creation.

As technology grew, so did the secrets. It wasn’t just bonus levels and special screens anymore. Developers started adding completely separate zones, exciting new worlds, and most importantly, specialized enemies. Hidden bosses quickly became the stuff of video game legend. Conquering these secret foes gave players some serious gaming street cred. As each AAA release is unveiled in the new age, gamers are hungry to comb each area in hopes of finding a secret boss to defeat.

Before the boom of the internet, secret bosses were discovered through word of mouth and gaming magazines. Today, players can access an abundance of information instantly. Because of this, it’s hard to talk about bosses that are “truly secret” anymore. As soon as a new boss is discovered it will spread through the internet like wildfire.

Still, there are some bosses that remain a little more hidden than others. We scoured the web (and our personal experiences) to compile a list of 15 hidden bosses you may not know about. Most of these foes are incredibly strong, featuring brutal attacks.

Who is your favorite? Let us know!

15 Kaarstag (Skyrim)

There are a lot of hidden bosses scattered throughout the land of Tamriel. You’ve got Vulthuryol, The Reaper, and the Ebony Warrior, just to name a few. But one particular Skyrim secret boss stands out among the rest. We’re talking about Kaarstag, a mighty frost giant first introduced during Morrowind: Bloodmoon.

If you’re feeling especially masochistic, you can summon this hulking spirit in the Dragonborn DLC. In the north-western area of Solstheim, you’ll find the ancient ruins of Castle Kaarstag. Near the back of the glacial cave, you can find and loot the giant’s skull. By placing it on a nearby throne, you can summon the behemoth. Be warned, the specter is no pushover. Kaarstag is level 90 and provides one of the greatest boss-based challenges in all of Skyrim.

14 Slot Machine (Star Fox SNES)

A lot of you younger gamers may remember playing Star Fox 64 on the illustrious Nintendo 64 and reveling in how wildly entertaining it was. Before Fox McCloud and crew became an N64 classic, they started out on the Super Nintendo. The SNES version was ambitious for its time and featured a “scrolling” game world that appeared 3D.

It also featured one of the craziest boss fights in any SNES game. By performing a series of odd tasks and then flying into the mouth of a hidden Phoenix (in the Asteroid Belt level), you’ll end up in the Out of this Dimension! zone. At the end of this spaced out journey lies a Slot Machine. In order to defeat it, you’ll need to shoot the handle until three 7s line up. Your reward is an eternity in this smiling moon paradise, as the level never ends.

13 Moon Presence (Bloodborne)

Some of the bosses featured on this list are hidden rather well. The Moon Presence from Bloodborne is a great example. Although it’s spiritually part of the “Souls universe,” Bloodborne is very much its own adventure. It’s a wild place, filled to the brim with Lovecraftian nods, morbid scenes, and downright terrifying enemies.

The Moon Presence is disturbing in its own right, featuring an array of Cthulu-like tentacles and a void-like face. This boss means business and will challenge all of your skill and ability. To unlock this benevolent beast, you’ll need to perform a series of tasks in a specific order. First, you’ll have to deny Gerhman’s request, then consume three of the four obtainable “One-Third of Umbilical Cord,” then finally defeat Gehrman, The First Hunter. Be warned, the Moon Presence will attack as soon as Gehrman falls, so you won’t have much time to prepare.

12 Father Rodin (Bayonetta)

Bayonetta is a wild world filled with angels, demons, and some spectacularly imaginative locations. During Cereza’s journey, you’ll find yourself frequenting “The Gates of Hell.” There, you’ll meet a mysterious gentleman named Rodin. He acts as the bar’s proprietor, which is also the front of an “underground” demonic weapons shop.

What you may not know, is who Rodin really is. Once a prominent angelic smith, he created numerous weapons and armors for the world of Paradiso. He was eventually exiled to Inferno, with some speculating that the angelic powers feared his strength and wisdom. By collecting almost eleven million halos, you can purchase a Platinum Ticket from Rodin. This leads to a cutscene where the Infinite One remarks about returning to his true form. You’re then instantly transported to an arena, where a battle against the most difficult enemy in the Bayonetta universe begins.

11 The Cow King (Diablo 2)

Back when Diablo first hit PC, a wacky rumor spread like wildfire. According to some adamant gamers, you could access a specialized Cow Level where you’d face off against an abundance of bovine baddies. These particular rumor proved to be false (much to the chagrin of everyone) but Blizzard took note of its fame.

In Diablo 2, the developer gave the gaming world what it wanted, hiding a secret Cow Level that could be accessed by combining Wirt’s Peg Leg and a Town Portal Scroll in the Rogue Encampment. Here, an abundance of weapon-wielding cows will hunt you down. You’ll earn bragging rights if you defeat the powerful Cow King secret boss but many suggest it’s better to leave him be. Leaving him alive will allow you to return to the Cow Level, which is a pretty solid grinding spot.

10 Reptile (Mortal Kombat)

Reptile deserves a spot on this list for two reasons. For one, it was incredibly difficult (for the time) to access him, and two, his fame pushed him from secret boss to fully playable character in the franchise. After Mortal Kombat launched, rumors began flying about a mysterious “third ninja” (aside from Sub Zero and Scorpion) that would appear if a certain set of parameters were met.

It turned out that the legend was real but accessing it took focus and skill. The only way Reptile would appear is if you were able to get a double flawless victory (complete with a fatality) on the Pit Stage. These conditions had to pair with a moon silhouette which only activated every sixth game. Reptile was a formidable secret boss and would become a playable character in Mortal Kombat II. He’s now one of the most prominent parts of the Mortal Kombat roster.

9 Culex (Super Mario RPG)

Super Mario RPG: Legend of the Seven Stars was a pleasant surprise. Gamers were already familiar with Super Mario Bros. and Final Fantasy well before this title released. Super Mario RPG blended the best of both worlds, giving us the active time battle we all craved, with the hilarity and originality of the Mario universe. After playing this release, you wouldn’t be surprised to hear it was released as a combined effort from Nintendo and Squaresoft.

The influences are easy to see but developers hid a very Final Fantasy-esque boss inside Monstro Town. After collecting a shiny stone from a girl in Moleville, you can open a locked door in Monstro Town. Behind it lies Culex, a boss that looks very out of place in the Super Mario RPG universe. He’s incredibly challenging and even features Final Fantasy IV boss music.

8 The Nameless King (Dark Souls 3)

The Dark Souls universe is packed full of secret bosses and hidden content. There are a lot of branching paths to explore. It was hard to decide what particular boss would pop up on this list but The Nameless King barely edged out the competition. His overall look and entrance are truly epic, making him a secret boss encounter you’ll never forget.

The Nameless King isn’t hard to find. You can summon him at Archdragon Peak, calling him from the skies by ringing the large bell (located in the Great Belfry) when it becomes available. The imposing figure will swoop down atop a large dragon, engaging you immediately from his draconic perch. Once you slash at the beast’s legs enough, the fight transitions to a one-on-one battle between you and this rather difficult (that’s saying a lot for the Souls Universe) hidden boss.

7 Ozma (Final Fantasy IX)

The Final Fantasy series is absolutely overflowing with side quests The main storyline (for many games) may be around 30-40 hours, but you can easily rack up 70+ finding and completing all of the applicable side missions. In fact, the series is so jam packed, we had to feature two hidden bosses on this list. The first is Ozma, a brutal spherical enemy from Final Fantasy IX.

To find Ozma, you’ll have to farm the agonizingly tedious Chocobo Hot and Cold mini-game. Once you locate enough Chocographs, you can teach your feathered friend the Sky Ability. From there, you can leap to the Chocobo’s Air Garden and find Ozma. Be warned, this is one of the worst fights in the entire game. Some unfortunate instances (like dual Meteor) will wipe your entire party in an instant.

6 Iwajira (Borderlands: The Pre-Sequel!)

Anyone who’s ever played through the Borderlands series can attest to the powerful allure of loot. Guns and shields are the name of the game, and although there is an underlying storyline, you’ll usually find yourself hunting endlessly for that one special weapon. This usually entails taking down big baddies in the hopes that they’ll drop some unique gear.

In Borderlands: The Pre-Sequel!, you can find a rather impressive farming location. A hidden boss, dubbed Iwajira (a Godzilla-like reference) is a towering kraggon that can be killed over and over for its delectable loot. Iwajira is located in a secret area called Pyroclast Grotto, which is south of the fast travel station at Serenity’s Waste. The boss himself follows a pretty predictable attack pattern, so he’s easily farmable once you learn it.

5 The Lingering Will (Kingdom Hearts II Final Mix)

This one is a personal choice on our part. A lot of people may have expected to see Sephiroth here. While the iconic Final Fantasy VII villain is a huge challenge in the Kingdom Hearts universe, we felt like The Lingering Will is a much more imposing foe. During Kingdom Hearts: Birth By Sleep, we see Master Xehanort possess Terra. During the struggle, Terra manages to bring to life his armor, instilling it with The Lingering Will.

After completing Kingdom Hearts II Final Mix, you’ll find an access portal in Disney Castle. Going through it will bring you face to face with this powerful entity. This is easily one of the hardest fights in the entire Kingdom Hearts universe (yes, even more so than Sephiroth). Hopefully, we will see another appearance by The Lingering Will in Kingdom Hearts III.

4 Night Terror (Soulcalibur III)

The Soulcalibur series isn’t as well-known as Mortal Kombat, Street Fighter, or Tekken, but it’s an incredibly engaging and entertaining fighting franchise. Soulcalibur III introduced players to a unique story mode (Tales of Souls), that helped shed light on the rich lore and expansive storyline that developer Project Soul created. Many players rifle through this mode and complete the final boss, without ever knowing that a hidden “true” final boss exists.

By taking a specific path through Tales of Souls (which varies with each fighter) and not losing a single match, you’ll come face to face with Night Terror. He’s said to be the true personification of the Astral Chaos. It’s impossible to ring out the towering character, thanks to a special set of wings on its back. Night Terror is supremely challenging and defeating him will unlock his profile and concept art. Sadly, he’s only playable by means of a cheat device.

3 Yama (Spelunky)

For the most part, Indie games are hit-and-miss with the gaming community. They’ve grown exponentially in recent years and sometimes an Indie release is so amazing it cements itself in the gaming hall of fame, alongside AAA titles. Spelunky is one such game, receiving critical acclaim for its entertaining and challenging gameplay.

If you’re skilled enough to make it to the final level, you’ll face a huge boss named Olmec. This isn’t the only massive baddie plaguing the Spelunky universe. Through a series of crazy prerequisites (including finding items, killing bosses, and defeating the final boss in a specific spot) you can gain access to a special zone called Hell. If you manage to find your way through the inferno, you’ll meet Yama, Spelunky’s greatest challenge. This behemoth king will test all your skills but besting him will earn you an achievement and a new character.

2 Baron K. Roolenstein (Donkey Kong Country 3)

Here’s another nod to a classic retro release. Donkey Kong Country 3: Dixie Kong’s Double Trouble is a SNES release with a lot of charm. The title is pretty lengthy and features a lot of frustratingly fun levels. It also plays host to a hidden zone (complete with a secret final boss) that originally tortured players with its possible existence. The island of Krematoa is real but it’s a pain in the neck to access.

Once you gain the Hover Craft or Turbo Ski, you can drive precise circles around four special rocks in order to raise the sunken island from its watery depths. Summoning Krematoa is only half the battle, as you’ll need to collect every single bonus coin in the game to face the final boss. This iteration of Baron K. Roolenstein is annoyingly difficult at first but shouldn’t be a problem once you figure out his mechanics and attack pattern.

1 Penance (Final Fantasy X)

Square did a great job crafting a brutal hidden boss (Ozma) for Final Fantasy IX. They completely outdid themselves with a secret boss in Final Fantasy X. Tidus and crew face many challenging enemies throughout their long journey. Once the group manages to leave Bevelle, a powerful group of Dark Aeons appears to derail their quest.

If you manage to fell all of these tough enemies, you’ll unlock access to a strange pillar-like foe named Penance. He may not seem like much at first glance but Penance is easily the toughest enemy in the Final Fantasy X universe. He boasts an insane 12,000,000 HP and has an array of punishing attacks. Two separate arms stand at his side, each with 500,000 HP (they also regenerate after a few turns when destroyed). Penance’s Ultimate Attack “Judgement Day” can hit your entire party for 99,999 damage and drain 999 MP.