Paper Luigi X though: either Luigi messes something up or the boss literally is hard and poses a legitimate challenge.
The Lone WolfGamebook series got progressively more difficult around book eight or so, but never really reached this level of madness... except for The Prisoners of Time. In addition to the usual death traps and Random Number God bullshit, there were three extremely difficult fights right at the end. In the first, if you brought the Infinity+1 Sword from an earlier book, the boss' stats were nearly impossible to overcome. The second featured similar issues, regardless of equipment. And the third was on the next entry, giving you no chance to heal, and you started by taking unavoidable damage.
Fictional example: "New Cap City" in Caprica. A DieselpunkCyberspaceMMORPG in which almost every player and NPC acts like a Hair-Trigger Temper psychopath, fighter planes randomly strafe the streets every so often, and dying once doesn't just permanently destroy your character but bans you from the game for life. And then the incredibly pissed-off AI teenage girls with God Mode powers and Resurrective Immortality turn up...
Most puzzle- or skill-based toys are simple once you get the trick. However, there are a few that remain fiendishly difficult, even after hours of practice. Worth special mention is Labyrinth, in which the object is to navigate a marble through a maze by using the knobs on the sides to tilt the maze itself. It wouldn't be that hard, except that the platform has a bunch of holes in it in addition to the walls of the maze. Falling through a hole forces you to start over, and all it takes is a momentary lapse in concentration.
There is now a 3-dimensional version called Perplexus, which is a ball encased in a clear plastic sphere with many obstacles. This one offers points to start from in the middle, but also many new challenges.
Homestar Runner parodied this trope. There's the easter egg game "Super Kingio Bros," in which you cannot possibly avoid the first enemy, who you find within the first second of the game.
Real Escape Game is a series of Room Escape Games, except in the real world—you are physically locked inside the room with a team of other players and have to find the key to the room to escape within the time limit. Most if not all versions of the game have clear rates of less than five percent. Even with a full stock of teammates, you'll need to think swiftly and outside of the box if you so much as want a chance at victory.
Finnegan's Wake, a book positively saturated with double meanings and confusing language. You need to read a guide just to understand any given passage. For reference, here's the first sentence:
riverrun, past Eve and Adam's, from swerve of shore to bend of bay, brings us by a commodius vicus of recirculation back to Howth Castle and Environs.
Harvard University's "Math 55" course is, by the university's own admission, "probably the most difficult undergraduate math class in the country": it covers several years of undergraduate math in two semesters, with the homework per week taking well into the double digits in hours and only a few students typically remaining at the end. The faculty deliberately made the course so difficult not simply as a weeder but to give students a new understanding of depth.
The Boston Marathon is widely known as exemplifying Nintendo Hard in road races. First if running 26.2 miles wasn't hard enough, to limit the number of entrants one must qualify for the race by first meeting a challenging benchmark time in another marathon. Then, while the Boston Marathon course features an overall elevation drop, the undulating New England terrain includes frequent uphill segments including several late in the race located precisely at the point where human runners are at their most vulnerable.
The Monaco Grand Prix is the hardest, if not one of the hardest, tracks for F-1 racers, since it consists of twisty windy city roads that two cars are barely comfortable in side by side. In fact, it's the only course that's given an exception to F-1 track rules (which most is laid out for safety reasons).
The Royal Navy's Submarine Command Course is informally known as "Perisher". It has been running since 1917 and has extremely high standards - the US and Danish Navies often send their officers to train on the course. Although the historical pass rate is around 70%, candidates who fail are immediately taken off the training boat and barred from serving in Royal Navy submarines ever again. In most cases this means the end of their naval career, so the course only attracts the most competent candidates.
The AIM-4 Falcon guided missile (used in Vietnam) was infamous for how it hard was to lock; it required seven seconds to establish a lock, which is no easy task when you and your target are whipping through the sky at Mach 1. The missile was also rendered useless if the user failed to achieve a lock the first time, as it had a limited supply of coolant for its targeting sensor. In a twenty year service history, it had only five confirmed kills. Its successor, the AIM-9 Sidewinder, is a significantly more effective (and easier to use) missile.
Real Lifeas a whole is this. Many aspects of life, from difficult education classes to trying to manage enough income to have a roof to live under to even just trying to stay alive can be challenging, depending on a variety of circumstances such as one's geographical location, bodily disorders, political and economical climate, and the way one is brought up (especially setbacks such as Abusive Parents). To quote an old cliché: Life isn't fair.