Nothing will ever top playing Halo 2 Legendary for me, legitimately the hardest game I've ever played, and one of the most frustrating experiences I've had in a video game.
Dbz budokai 2 when I was a kid, that game killed my soul, it was so difficult for me at the time
Destiny 2. The crucible
League of Legends. I think I swore off competitive multiplayer games after that.
I found League of Legends boring as hunting for clams.
Phantom 2040 for Sega Genesis. Took me forever to figure out all the right choices, strategy, and tactics. I love that game.
Dead Cells, I don't like wasting time