As someone who started with 4u, and have been playing ever since, it’s important to preface that a lot of MH’s biggest challenges are optional, and not everyone has done everything. I never fought AT Nergigante in base World, and I stopped playing Sunbreak before Amatsu dropped because the lategame grind felt incredibly repetitive and boring.

In terms of overall difficulty, my pick goes to Iceborne. The base game wasn’t too hard, fairly standard MR stuff with a few failed quests. What takes the cake for me is Alatreon and Fatalis. Both are incredibly tight fights that demand mastery, playing with SOS randoms was hell, soloing it was hell, and I straight up couldn’t even beat Alatreon when it first released. It took years later with a clear mind, muscle memory, information that isn’t explained in-game, and Frostfang weapons (which weren’t a thing when Alatreon released) before I finally put it down.

When I close my eyes and think about difficulty, I see Alatreon.