I think its when Meng Hao fuses with a number of legacies or something like that. It starts with i am immortal number ? (various numbers) or something like that.
Only one legacy: Blood Immortal legacy. Around chapter 119, just go forward or backward a few chaps from there till you get the chapter you stopped at.
Actually I think he's referring to soemthing else Spoiler The Grand Dragoneer legacy of the Frigid Snow Clan in the Black Lands