Megaman X 6 on PlayStation and Megaman X 7 on PS2. Both horrible games, both equally hard for no reason whatsoever.
I honestly didn't have much trouble with X7 outside of that fire boss(BURN TO THE GROUND). He gave me a lot of trouble for some reason.
As for X6: I only have trouble in like two stages. 1. That stage in Gate's castle where you have to navigate spikes. 2. The optional section of Metal Shark Player's stage has a shit ton of spikes as well.
Otherwise I found X5 harder because of the insane time limit.