IGN interviewed the player a few weeks ago:
In the grim, unforgiving world of Elden Ring, there are no characters that can truly be considered heroes — not even the protagonist. But one community member has risen to fame in the last week: a naked man wearing nothing but a jar on his head who waits outside the door to the game's hardest boss under the polite request of a name: 'Let me solo her'.
Let Me Solo Her (who asked in an email to go by either his Elden Ring moniker or LMSH for short) is an unassuming, altruistic player who has been dropping his summon sign outside the boss fight door of Malenia, for the last week or more. Malenia, while not a mandatory fight for finishing Elden Ring, is the culmination of multiple sidequests and has become notorious in the community as one of the most difficult battles FromSoftware has ever designed. So naturally, there are plenty of players who feel they want to finish it for completion, but are struggling to do so.
While Elden Ring is largely a solo adventure, players can opt-in to co-op using certain items that will reveal "summon signs" — gold markings on the ground that allow them to call other players (who have opted into being summoned) to their games and work together until a dungeon is completed, a boss defeated, or someone dies. In LMSH's case, he simply drops his summon sign outside Malenia's boss door and, once called upon, heads inside the boss chamber and immediately proceeds to wreck Malenia without anyone else's help. This both allows whoever is hosting him in their game to get the kill and move on with the story, but also provides a hell of a show.
Obviously at this point they know exactly how to handle every attack, etc, but notice that they have a ton of vigor, high rune level, very powerful weapon selection (and are running bleed + frost to trivialize questions of DPS so they can solo as a summoned player)— Bruno ☠️ Dias (@NotBrunoAgain) May 10, 2022
They chip in damage in very well-understood windows and are happy to simply not be in the same zip code as several of Malenia's attacks. It's a very achievable strategy for others to follow, especially for a boss like Malenia that punishes getting hit so harshly.— Bruno ☠️ Dias (@NotBrunoAgain) May 11, 2022