Join The Club
I've always been deeply impressed by Final Fantasy 14's solo only challenge runner RathGames—who has been working through the MSQ on his lonesome. Or, as much as is possible given the circumstances. See, FF14 is an MMO, it's not meant to be done on your own, there are explicitly mechanics, encounters, damage checks that are designed for a full party of four to eight people.
Furthermore, RathGames refuses equipment from quest rewards, making most of his gear himself—the one time he's had to renege on his promise was within the Crystal Tower, in which he assembled a group of other solo-only challenge runners because the game quite literally wouldn't let him inside otherwise.
The other time he's technically broken the rule of the run was recently with Shadowbringers' Hades fight. Though I'll say he did so by the letter of the law, not in spirit. RathGames beat that duty with a second character, but he multi-boxed between them by alt tabbing without any external programs, and he levelled that second character all the way through the MSQ a second time without help.
Alas, it didn't take long for RathGames to hit another wall—the Seat of Sacrifice, a battle that has a massive group-based check: Ultimate Crossover, wherein Elidibus throws a Limit Break 4 at the party. Usually, you need to counter this with a Limit Break 3 from a tank, but given RathGames doesn't have access to those, it wasn't looking good.
Thus once more came his alt character, Solo Savior, to the rescue. Rather than trying to out-DPS the fight so that Ultimate Crossover never triggers, RathGames instead showed up to multibox with his main as a Blue Mage, and his alt as a Sage—a healer.
Blue Mages are a 'limited job' with a bunch of gamebreaking spells and, as such, aren't usually permitted in group content (but viable via an unrestricted party). They can obtain an ability called Self-destruct, which does what it says on the tin. Rath waited until Elidibus began casting Ultimate Crossover, had his Blue Mage main blow themselves up, and raised them with his Sage.
Because raises in Final Fantasy 14 have a grace period of one minute, and a brief invulnerability window after the target's resurrected, Rath was able to skip the mechanic entirely by timing his main's acceptance of the raise spell, being either in the raise animation or invulnerable for the oncoming damage.
He only had to do this once, mind, given the fight gives you a checkpoint afterwards—but still, the amount of preparation needed is immense, and it's not as though the rest of the fight was a cakewalk, either.
What ensues is a delicate dance where Rath has to use the Blue Mage's diamondback spell to avoid certain death, occasionally raising his sage alt (who spends most of the fight dead) to deal with other mechanics, usually causing them to immediately die afterwards while his Blue Mage lives on.
It's another incredible feat, and one that took multiple arduous streams just to theorycraft and tackle. Rath's determination in the face of absurd, self-inflicted (a little worryingly so) odds continues to be an inspiration.
