None, I'm a gaming masochist and I beat every NES 2nd quest; SMB1, Zelda, Metroid, Kid Icarus, Mega Man, Contra, Rush-n-Attack, Ikari Warriors, Iron Tank, Castlevania. Including some truly brutal ones like Legendary Wings, Gunsmoke, and Astyanax.
The more difficult the better.
I leveled a Discipline Priest in vanilla WoW on the Alliance side of a pvp server. I played a pvp thief in Ultima Online with no magic skills. I ran melee through Diablo hardcore hell difficulty. I played through Goldeneye and Perfect Dark on the highest agent settings. I beat the original Aliens vs Predator before the patch allowed save games. Serious Sam 1 and 2 were owned on Serious mode.
I play Nethack without copying save games, I play DWARF FORTRESS and always start in scary zones.
Bring it on.