The title of the DLC discussed in the news is "Shadow of the Erdtree" for the game Elden Ring.
The boss beater mentioned in the article is Let Me Solo Her, who recently rebranded as Let Me Solo Him to fight the expansion's tough boss, Messmer, in Elden Ring: Shadow of the Erdtree.
The tough boss in the Elden Ring: Shadow of the Erdtree DLC is Promised Consort Radahn. He is considered one of the hardest bosses in the game and possibly in the entire Soulsborne series due to his aggressive attack patterns, area-of-effect attacks, and the support he receives from Miquella in the second phase of the fight.