Allright. Here goes.
The Legend of Valis 3: It's a pretty obscure game, but all you need to know is that  you have 3 main abilities: attack, slide, and jump. But it's one of those overly vertical, jumps that barely let you get to he other side of a chasm, let alone come back.  And it had an ice level that required you to slide under spikes, in a small moving platform over a endless precipice, while bouncing ice crystalsthreaten you. You slide wrong, you die. You don't slide you die. A bouncing ice cristal hits you, you fall  off and die(any hit sends you reeling back). I never made it that past that level.
The game Fighter's Destiny(take a guess at the genre) has a challenge featuring a cow, called Ushii. I think it was a Rodeo mode. You had to  avoid getting knocked out of a small square. THe Cow saw incredibly fast and It felt impossible at the time.
Street Fighter Alpha 3. The boss was not only 
Capcom cheap(R). But the game surprised me with it's ONLY ONE TRY POLICY! How was I supposed to know!?
Teenage Mutant Ninja Turtles: Tournament Fighters(Genesis). Karai, the final boss would shoot a projectile, headflip over you, and launch a full on high speed combo attack on you. EVEN if you hit her befor she hits you, that projectile is STILL coming for you. And since this game's blocking system doesn't cover any sort of grab or hold, ever,  she can grab you and supplex you. If she does, it might as well be over. Getting up takes so long, one can win a fight by throwing a player AS THEY RECOVER FROM A FALL and repeating until death comes.   I won by pausing the damn thing until I found an opening. Of course,the grabbing 
 tactic works on her as well...