For players who want games to challenge them, Xbox Game Pass has a decent amount of titles that are more than happy to deliver on that front. Here's a selection of the longest, hardest, and most challenging Game Pass games.Difficult and lengthy games are far from rare on Xbox Game Pass, with a host of titles that will see achievement hunters playing for thousands of hours, having their skills fully tested, and/or putting their luck to the test against the RNG gods. One crucial thing to look out for when considering starting one of these demanding games, though, is whether they will stick around on Game Pass long enough for you to get the completion. Starting something like Deep Rock Galactic — which will take hundreds of hours and has been on Game Pass for over two years at this point — could be pretty risky, since an imminent announcement that it's dropping out of the Game Pass library could leave you without enough hours in the day to physically get it done in time. First-party titles are typically exempt from this as they're usually around for good (although watch out for server closures and such in older games), but as long as you're mindful of the time you're likely to need versus the time you're likely to have, there's plenty to get your teeth into on Game Pass.
Since we often put out articles about how to stock up on Game Pass easy achievements as well as Xbox sales quick completions, we thought it only right to redress the balance a little. We'll use the same kind of logic — so a focus on full achievement completions, perhaps with the odd exception — and largely write off anything where stuff like unobtainables make for an impossible completion (sorry, Nuclear Throne, I still love you). So here's to the hardcore hunters keen to tackle epic games like these... may the thrill of that final gruelling achievement pop live long in the memory!
Microsoft Flight SimulatorDifficulty type: Grind
We typically wanted to steer clear of games that cannot be completed for this article, and while that's technically the case for the Xbox version of Microsoft Flight Simulator, it didn't seem right to leave out a game that has an achievement for racking up 1,000 hours of flight time. The offending achievement for console players is Decathlon, and while completing ten weekly activities might not sound so bad, turns out it's not that easy when the team doesn't actually run weekly events — there have only been a total of four for console players since the Xbox version launched in mid-2021, although shared progress with the PC version (which counts a second time for achievement progress here, too) means it has been possible for console players who also have a decent gaming rig to work through this despite the shortage of events. Even ignoring this achievement, the majority of the rest of the list has unlock rates well below 5% on TA (and much lower globally) and we have just 25 completions on-site from a player base of over 100,000... this one will take some serious dedication.
Microsoft Flight Simulator Standard 40th Anniversary Edition
From light planes to wide body jets to gliders and helicopters, fly highly detailed and accurate aircraft in the Microsoft Flight Simulator 40th Anniversary Edition. The world is at your fingertips.
The Standard 40th Anniversary Edition features 37 airplanes, gliders, and helicopters with unique flight models, 25 handcrafted airports, 4 classic commercial airports, 14 heliports and 15 glider airports.
Sea of ThievesDifficulty type: Grind, luck
Casting aside its 13 discontinued achievements after the Arena mode was scuppered, Sea of Thieves is an absolute whale of a completion even just looking at the base list, let alone the achievements added in its 20+ title updates. The base game alone has a completion estimate of over 1,000 hours, and while a lot of it isn't too bad (especially with a reliable crew), there are a bunch for various in-game Commendations, most of which sit at around a 1-2% unlock rate here on TA. Each of these requires a huge amount of time working on specific activities or with certain factions so there isn't an awful lot of overlap, and just working your way through these will likely take months — unless you've got a permanent crew to play with and/or amicable 'adversaries' on alliance servers with whom to boost, you're also going to be at the mercy of the fates in terms of what other players get up to with and around you, so things can often be out of your hands in a game this chaotic. Title updates have also added many more Commendations and related (and unrelated) achievements to the game, so there's even more stuff vying for your time, and it doesn't stop coming. Good luck if you're only starting on this voyage now... you've got almost five years' worth of catching up to do.
Sea of Thieves
Sea of Thieves offers the essential pirate experience, from sailing and fighting to exploring and looting – everything you need to live the pirate life and become a legend in your own right. With no set roles, you have complete freedom to approach the world, and other players, however you choose.
Whether you’re voyaging as a group or sailing solo, you’re bound to encounter other crews in this shared-world adventure – but will they be friends or foes, and how will you respond?
Crusader Kings IIIDifficulty type: Grind, luck
Something a little different now, but Crusader Kings III still puts up a challenge for the ages. A lot of this comes down to just how much is going on outside your control — the best of plans and intentions when working towards a specific achievement could crumble to dust if a key figure suddenly becomes impotent, gets abducted, or is just straight-up assassinated. Since many achievements only unlock in Ironman mode, it's not even like you can easily save-scum your way around a lot of these unforeseen events either. The list demands all kinds of very specific tasks, some you may luck into during any given run, and others which might keep you busy trying to do one particular thing for generations. You also need to factor in that grand strategy games as ridiculously deep as this aren't exactly the easiest things to just pick up and play — coming into a game like Crusader Kings III fresh, it'll likely take you hours to even just find your bearings before you even understand the systems required to get a lot of the achievements. With less than 100 completions on TA from a player pool of over 20,000, it should be pretty clear that this won't be easy to conquer, so godspeed, my liege!
Crusader Kings III
Lead a medieval dynasty through the generations, as history swirls around you. Rule a small realm or a major empire, encountering a dazzling number of characters with unique personalities and priorities in this award-winning strategy game from Paradox Interactive.
Gears seriesDifficulty type: Grind, skill
You can't have a list like this without mentioning the Gears series — a franchise renowned for one recurring achievement that is the very definition of grindy, backed up by stacks more that will keep you busy across all modes of each game. Any and all mainline Gears titles could sit in this spot, but if we absolutely had to pick one at Lancer-point, Gears of War 3 would be the play — Seriously 3.0 really upped the ante for this gruelling achievement, turning it from just grinding out kills to grinding out absolutely everything by requiring all Onyx medals. Shoutout to Gears 5, though, for having the audacity to split Seriously into two brutal achievements and dropping the second in a title update nearly two years after launch. The first two games' lists look positively tame in comparison to those that came after (bar Judgment), so those might be good starting points if you're tempted to get a Seriously achievement on your tag but don't want to commit thousands of hours to it.
From one of gaming’s most acclaimed sagas, Gears 5’s celebrated campaign and refreshed multiplayer are fully optimized for Xbox Series X|S. With all-out war descending, Kait Diaz breaks away to uncover her connection to the enemy and discovers the true danger to Sera – herself.
Unravel TwoDifficulty type: Skill
This one's for Game Pass Ultimate subscribers, since Unravel Two isn't in Game Pass itself, rather part of the EA Play library and available with Ultimate. Now you might not have expected to see a cute platformer about some little yarn dolls wedged between Gears and Ninja Gaiden on a rundown of rough completions, but here it is — if you know, you know. Unravel Two's cuddly exterior hides an achievement list capable of testing any player, with deathless and speedrun achievements for each of the game's main levels (as well as the bonus stages), plus a handful of extremely specific ones you'll likely need to practice as well. Those speedruns are no joke, with very little room for error on the gold medal times, so the trickier ones are likely to take quite a few attempts and require learning unique tricks and strategies to buy you a little breathing room. All of these sit at a crazy 0.02% unlock rate on Xbox (and sub-1% here on TA), which should give you an idea of just how tough these are — most regular players haven't even seemed to bother to try and do them, so it falls to the achievement hunters to drag those percentages up as they shoot for the completion in this surprisingly savage platformer.
When you cut ties to the past, new bonds form. In Unravel Two, create relationships with other Yarnys in local co-op or as a single player, fostering friendship and support as you solve challenges together. Chase the spark of adventure through stunning landscapes to watch your surroundings blossom with new life.
Ninja Gaiden seriesDifficulty type: Skill
As with Gears, there's probably no factually correct answer as to which game from the Ninja Gaiden series should claim this spot — different players will likely struggle with different aspects of each — so it makes more sense to cover them as a job lot, especially since that's how they're included in Game Pass as the Master Collection. Team Ninja's franchise is famously brutally difficult to the point that a lot of players will struggle to get through the games on a casual run, let alone manage to pull off the wild feats expected of players looking to grab all of the achievements. All three games have under 100 completions each, from a total pool of over 40,000 players across the trilogy, with loads of troublesome achievements across the games for beating Master Ninja difficulty (and doing so with Master Ninja grades) and each game's various trials, all of which are known to be painful to get through. Similar games like Devil May Cry and Bayonetta tend to give you a lot more tools so you're a powerhouse by the time you take on their hardest modes — Master/Ultimate Ninja will throw you in against normal dudes who annihilate you in a couple of hits, not to say anything of how hard special enemies and bosses can hit. A Ninja Gaiden completion is a true feat of skill and perseverence, so we bow before anyone who has risen from the rank of Ninja Dog to Master Ninja with their sanity intact.
Spelunky 2Difficulty type: Grind, luck, skill
The original game got tons of love back in the Xbox Live Arcade era, so many who have been playing since the Xbox 360 days probably know of Spelunky's propensity to not pull punches. Spelunky 2 continues this tradition and perhaps takes it even further, with its levels and myriad hazards different every time you play so you can never really fall into a proper groove and are constantly thinking on your feet. Just a cursory glimpse at the Spelunky 2 achievements should tell you all you need to know — just five of the 32 achievements have a TA unlock rate of more than 10%, with most significantly lower. We've heard some people call Spelunky 'unfair,' which, ironically, is actually a bit unfair on the games. Yes, there are plenty of devious tricks and unfortunate layouts with which to contend and the odd cheap shot, but you'll eventually come to learn the ropes and go from bungling tomb raider destined to stumble face-first into every single spike trap to master explorer, deftly disarming traps with all manner of neat feats. Getting there will take some time, but damn, does it ever feel good when a run comes together.
Spelunky 2 builds upon the unique, randomized challenges that made the original a roguelike classic, offering a huge adventure designed to satisfy players old and new.
DescendersDifficulty type: Grind, luck, skill
Both Descenders and Unsouled below were nominees for June's TA Playlist, suggested by winners of our Great TrueAchievements Score Challenge — that should give you an idea of the kinds of ratios up for grabs in these games. Downhill biking game Descenders has just over 130 completions here on TA from close to 100,000 players, and covers all three categories here. Random level layouts and one achievement in particular bring the RNG factor, which in turn can lead to a grind as you bang your head against tricky stages hoping for a friendly seed, and of course there's a massive skill dependency since you're having to adapt to courses on the fly. When they say "extreme downhill freeriding," they really do mean 'extreme.'
Descenders is extreme downhill freeriding for the modern era, with procedurally generated worlds, and where mistakes have real consequences. Will you lead your team to glory and become the next legendary Descender?
UnsouledDifficulty type: Skill
Back when it was up for being a TA Playlist game, Unsouled had just one completion, by Infamous after using the then-recent Game Pass addition in the GTASC contest to score big. Since June 2022, that completion count has only risen by 20 despite the player base more than doubling in that time. Only the achievement for dying once has better than a 10% unlock rate on TA, but since so many achievements relate to the punishing Master Soul difficulty and things you'd have to go well out of your way to find, that might not be all that surprising — this is very much the kind of game where we see lots of Game Pass bloat from players trying it out and bouncing off very quickly, but the first death achievement means this one is on your card for good whether you persist or not. And persist you should, as considering one developer did everything on this hardcore action game, it's really impressive, especially if you give it the time it takes to fully learn its nuanced systems.
Take on the role of the Fallen Prince in Unsouled - a stylish, fast-paced 2D action-RPG. Fight your way through interactive environments and adrenaline-pumping encounters as you unravel the mysteries behind this world filled with the undead.
Halo: The Master Chief CollectionDifficulty type: Grind, skill
Halo 2 LASO. Need we say more? Yeah, we probably should... would run a little short otherwise. Compilations feel even more like cheating than including entire series, so we've limited ourselves to just the one (sorry, Rare Replay), and with a whopping 700 Halo: The Master Chief Collection achievements to go after, there was only ever one pick. Halo 2 Legendary's deadly Jackal snipers are just one of your concerns here, with six entire games' worth of solo and multiplayer content to work through on the way to the completion. LASO (Legendary All Skulls On) runs of all games will truly test your mettle, on top of which there are all manner of other achievements tied to difficulty, deathless levels, time trial runs, collectables, situational stuff, multiplayer, and just about everything else you can think of. It's a stacked list that serves as a comprehensive history lesson on the series that originally defined Xbox as a platform — with a little over 2,000 players with the full 7,000G from almost half a million TA players, this would make for a legendary completion to have on your tag. Hope you like Halo, because there's a lot of it here!
SpiderHeckDifficulty type: Luck, skill
It may be a daft party game about spiders fighting with laser swords, but SpiderHeck is clearly no pushover if only 0.1% of TA players have grabbed the completion so far. Like TowerFall, this chaotic multiplayer title also has a single-player/co-op component, and that's where the problem achievements seem to lie. SpiderHeck's Survival mode and challenges both have a string of achievements tied to them for progression through each mode, and looking at the steep drop-offs in unlocks at each step, it's tricky to know whether it's the lofty skill ceiling of the physics-based gameplay or the random nature of enemy behaviour, pick-ups, and stages that is holding folks back — truth be told, it's most likely a combination of the two. Still, SpiderHeck looks to be one heck of a ratio booster if you're willing to put in the hours and master its fiddly mechanics... nobody will want to play you in versus once you ascend to arachnid godhood, but that's the price you simply have to pay for being one of just a handful of people with this completion.
Spiders with laser swords! Swing, stab, shoot with style and cool parkour.
Pac-Man Museum+Difficulty type: Grind, skill
That bit about only including one compilation? Yeah, that was a lie, sorry. It just felt like this list was missing some retro love, and while again it feels like Rare Replay is getting short-changed here, it's with good reason. You see, Pac-Man Museum+ isn't just a tough completion because old games are famously hard, but also because a) some old games are really bad, and b) some conversions and ports are also really bad. Museum+ falls foul of both, with licensing issues preventing some of the better legacy games being included to help bolster the quality quota that Pac-In-Time drags down so very, very hard, and input lag issues making some of the faster games in the collection extremely difficult to play to the level required for the various Missions and achievements. Mastering a bunch of retro games isn't something you're going to do overnight, and on top of needing to do that, there are a good few extremely grindy achievements tied to the pretend arcade itself where all these virtual old games live to worry about. Even though Pac-Man Museum+ houses some stone cold classics, Rare Replay is the better collection, it must be said, but this is arguably the harder of the two... if perhaps not for the right reasons.
PAC-MAN MUSEUM+ includes 14 titles from the legendary PAC-MAN series!
Play a variety of classic and nostalgic PAC-MAN games across many genres!
The Elder Scrolls OnlineDifficulty type: Grind
Tom would kill me if I didn't include The Elder Scrolls Online here... then likely resurrect me and kill me again if I didn't mention the fact that he is one of a select few people to unlock the Emperor! achievement — you know, the ridiculous PvP one that serves as the gatekeeper preventing all but the most hardcore MMO players from ever getting this completion. With almost 6,000G on the table and estimates well in excess of a thousand hours, though, this more than earns its place here, even if you do have to shell out for expansion content (and invest those few thousand hours, of course) to unlock the lot. It's one of the best Xbox MMO games, sure, but gunning for this completion could end up being more of a career than a hobby given that the list is only going to keep getting bigger with every new content drop.
The Elder Scrolls® Online
Includes The Elder Scrolls Online base game and the Morrowind Chapter. Join over 18 million players in the award-winning online multiplayer RPG and experience an ever-expanding story in a persistent Elder Scrolls world.
Optimized for the Xbox Series X|S with Console Enhanced, bringing a new level of fidelity and performance—free for all ESO players.
Got any of these completions on your tag already? Or perhaps you're planning on taking one on soon? Anything else you think should have made the list? Let us know down below, and may the RNG gods smile upon you and your chokes be few!