Ugh, being the younger sibling or the visiting friend when it came to video game controller dominance was the worst. But not all secondary characters were created equal.
Nana - "Ice Climbers"
Being a girl was either amazing (because you were a girl and yay!) or awful (because you were a boy and ewww cooties!) but either way there was something cathartic about clubbing your way through baby seals, yetis and polar bears to get your eggplant back from that thieving bird.
Plus this was no cooperative game, more of a blood sport.
Oh sure, you could work together for the greater good, but like any great forced alliance, eventually one of you must die for there is only enough eggplant on this mountain for one.
Zitz - "Battletoads"
While a difficult game in its own right, Battletoads became nigh on impossible once the second player joined in. At first, one of you would accidentally kill the other one, then "accidentally," then all hell broke loose and it became a free-for-all of backstabbing.
Until you got to this level.
And then you turned the game off because two hours of rage-filled bike crashes are about all a human child can take.