i'm hestitant between 3 boss fights because they were all insanely hard for different reasons (all are solo'ed)
boss: ethereal queen
game: start ocean the last hope.
special circumstance: deal the deathblow with lymle and beat him within 10 minutes
explanation: the ethereal queen is the strongest superboss in the game by far and is located in the second (and last) post game dungeon of the game called the wandering dungeon. the wandering dungeon has 20 floors and obviously the EQ is located on F20 on all the even floors you will fight a boss (however the EQ is the only hard one) and the odd floors will have a random challenge picked out of iirc 3 possibilities, of which 1 is taking a lot of time. so the main part why this one is so hard is because of the major punishment when you lose: the WD itself is easy enough that you can expect to reach F20 with little trouble, however, to reach that point you have to play about 5-6 hours on average, which can vary in hours of time both more and less hours depending on which challenges you get on the odd numbered floors. and the thing is, you can't save in the wandering dungeon so you have to do this all in one run and death means everything you did was all for nothing and you have to start over the whole thing. you can leave voluntarily to keep the stuff you found but this also means you have to start from floor 1 again. as for the fight itself, there are several things that make this one quite hard: first of all, the boss itself is quite powerful. one of her attacks supernova is powerful enough to easily 1 hit kill your entire party, you can still switch players after but that still costs time and making mistakes often means you die again. but besides the raw power and obviously the pressure of dying and being forced to do the WD all over again. there are a few other things, you need to do more then winning, you have to do it within 10 minutes and deal the deathblow with lymle because there is a battle trophy (not to be confused with trophies) in game you will only get when you win the fight that way. and there is a trophy you will only get when you have collected all 900 battle trophies. so first of all, lymle is a very bad character for this challenge, the only good abilities she has are fire elemental but the EQ is immune to all elements, in other words you can't expect to win within 10 minutes while using her as your character, so you have to let some other character beat her up instead and switch when she almost dead, but the thing is the EQ has no health bar. so you kinda have to guess when to switch, so doing this too early measn you don't get it done within 10 minutes, and doing it too late means the deathblow isn't dealt by lymle. and even if you manage to win the fight but didn't meet those requirements you are forced to restart the game because if you try again she is literally twice as strong so you literally can't beat her within 10 minutes.
boss: four kings
game: dark souls 1
special circumstance: level 1 challenge on new game +
explanation: most people probably are aware of the difficulty of souls games, so imagine playing the whole thing at level 1. now imagine this is just the easy part since new game + is a LOT harder. usually my hardest boss of the game is dragonslayer ornstein & executioner smough. but because of the massive health and wide range of unforgiving attacks (which almost all of em 1 hit kill you) the four kings is easily the hardest one imo. usually blocking with your shield is the best way to prevent damage, but because all of his attacks (including his common sword swings) include magic damage you still get damaged when hit even if blocked. and you can switch to a better fitting shield but thats at the cost of stability which means your stamina drains much quicker when hit. and you can't take your time either because he will duplicate with getting a sword in your ass in the process. so rolling is the preferred option so you nned to time it really well in order not to get hit, and you need to know very well how his attack patters work or otherwise you can't roll right or you get blasted by his AoE attack or humanity grab which are both using up a lot of range.
game: monster hunter freedom unite
special circumstance: G rank gathering hall solo
explanation: monster hunter is a quest based game in which you get promoted to higher levelled quests when you complete the "urgent quest" which you can only unlock by winning several "key quests" the level of a quest is measured by an amount of stars and a bunch of those levels together are either low ranked, high ranked or G ranked. the difference of strength between the ranks is a lot. the majority of teh quests are "hunting quests" which means you get sent to a map where a boss monster lives and you have to kill it. there are all kinds of monsters but teh hardest one i have beaten till now is the rajang. it might not look like much but it's way stronger then several (gigantic) elder dragons i've already beaten. there are 2 main questlines in the game, you have the village questline and the gathering hall questlline in the village questline everything has to be solo'ed and in the gathering hall you have a choice to solo but you can also team up (max 4 players) as you might expect, the gathering hall questline is a lot tougher because its difficulty is kinda made for teaming up. however i always like to do it all solo and i only even consider teaming if i have completed a quest at least once. the main reason why it's so hard i because he has a combination of great speed, and great strength, he also has a lot of moves which vary from all kinds of directions meaning theres almost no safe spot where you can hit him. which means he's very hard to dodge and when he hits it's for a very great chunk of your health bar. have to say there are much more extremely hard quests i still plan on doing 😜
obviously i was really happy when i cleared these bosses under these conditions 😁