battle toads, all be it briefly ( couldn't get into it enough to justify putting up with its crap)
but i owned
TMNT 1 (beat it -.- fucking Technodrome)
Fester's Quest (hard, but not as hard as some)
Blaster Master (>.> i get to lvl 6 and i'm lost and boned)
Ninja Geiden, NES version, as its only one worth playing >.>, made it to 6-2, nuff said there
the NES hard game list is rather long, but then, its notta system for wusses
( no difficulty settings to speak of, 1 life games with no check points, and only a few continues if any in some cases)
more currently
Demon's Souls comes to mind, but not much else, i gave up in the ninja geiden games at sigma 1, for taking NG Blacks perfect difficulty, and ramping it up to unplayable -.-