Hardest from an initial playthrough standpoint might honestly be diamond/pearl because they had pretty bad level scaling throughout a lot of the game. Once you’ve played through it once it’s easy to prepare for the difficult parts though.

From a nuzlocke standpoint ultra sun/moon are also pretty hard because of the necrozma fight but again when you know it’s coming it’s honestly not that hard to prepare for.

I’ve never played through regular BW2 on hard mode but I’ve played through a sizeable portion of the drayano hacks (blaze black 2/volt white 2) in hard mode and those were pretty challenging.

Me going back to hollow knight, celeste, modded minecraft, and dead cells instead of buying new games

I believe in 2a and 5b Celeste supremacy. Aside from having the best soundtracks I also like those levels the most as well

Another funny concept