Getting the tate on Hiruko as Hotsuma on Super difficulty and S ranking the final stage in Shinobi (PS2)
Completing all of the combat challenges in Arkham Asylum. Combat was harder in Arkham Asylum than it was in Arkham City.
Beating all three Sigma forms in Mega Man X4 as Zero with no damage taken and without using the fire weakness against his first form.
Beating Mr. Freeze in The Adventures of Batman and Robin on the Genesis.
Handing Shredder his ass in Teenage Mutant Ninja Turtles on the NES.
The first time I finished the Tule Tree Tops and got the orb in Guacamelee. Now I actually find that challenge to be pretty easy.
Finishing that dam "The Final-Final Test" stage in Super Mario Bros. Wonder. I only did it with Yoshi though which almost doesn't really count. I know with enough attempts I can do it with Mario or Luigi but I just lost patience with it and wanted to move on to another game by that point.
Completing "What sort of game master are you?" on The Dishwasher: Vampire Smile and getting the "Twitch Game Master Extreme Ultra" achievement
Finished Golden Axe (Arcade version) with no deaths.
Finished Die Hard Arcade/Dynamite Dekka without playing the Deep Scan mini game for extra credits.
Finished every fight in Alice: Madness Returns with no damage.
Finished every fight in Narita Boy with no damage
Finished every fight in Crisis Core with no damage. Yeah, I have a thing for no damage runs LOL
Beat Volgarr the Viking, that game is hard as hell, but totally fun to master.
The first times I beat Ninja Gaiden, Mega Man, and Double Dragon III on the NES.