I beat both Gothic 1 and Legacy of Kain: Soul Reaver 2 without using a mouse, playing only with the keyboard. I found the camera so clunky in both of them that I just gave up on trying to control it.
Turned out to be a lot more fun than expected.

Also, pretty proud for beaing Ozma in Final Fanatasy IX without even trying and without the critter quest complete. After he trashed me a few times, I just booted the game in disgust and just went at it sure I'd fail. 20 minutes fight, but damn fun.

Sephiroth in Kingdom Hearts was, again, a very proud moment.

Lately I got the plat in some rather difficult games like: Velocity Ultra / Velocity 2X, Bloodborne and Shovel Knight (not difficult on its own, but you have to beat the game without dying and under 1h 30 min)

Never knew you could spray the jumping fish with Yoshi to create platforms in Ricco Harbor in Super Mario Sunshine. Got to the star after several hours and much pain, but I did it...

Also beat Battletoads for the NES and ZombiU on survival mode.