So, every system (well, most every) has its 'system sellers' and your absolute favorite games, but for you, personally, what games really 'define' a particular Nintendo system for you? It doesn't have to be your favorite, your first, or even a particularly good game - just the game that really speaks for the system it was originally on?
I'm going to pick two (for now). Nintendo 64 - Mario Kart 64. If you try to play this game now, it's horribly ugly and near unplayable (particularly in 3/4p modes 1/2p isn't *that* bad) - but the 3/4p modes where what sold this game (and, in my case, the system) It was a quck pick-up-and-play game that up to four people could play with virtually no skills needed *and* really showed (in my opinion at the time) a huge difference between the previous iteration without completely changing the game itself. When most people list off the 'must have' N64 titles, they go with the Zeldas, Mario 64, Goldeneye/Perfect Dark, Smash Bros., and if Mario Kart gets mentioned, it's usually in a list of various Mario spin-off titles (Tennis, Party...) that are worth getting if you get a good deal. And with good reason - it just hasn't aged well. But it's still what I consider a defining experience for the N64.
Then, Game Boy. Now, everyone knows the indisputably best game of all time ever (Link's Awakening) came out on the Game Boy - and, of course, there's Tetris and Pokemon, two completely different types of games that changed the landscape of gaming for years to come (until they were merged into Pokemon Go) - but there's really one game that, strangly, defines what the Game Boy is for me, even though I still don't own it to this day (and thus was kinda the inspiration for this post) - Motocross Maniacs. I wasn't even sure of the title and had to google "Game Boy Excitebike" to find it. I played a metric crapton of this game... at Target, on the display unit, before I was lucky enough to get my own Game Boy. Easy to play in spurts, fun, addicting, and the graphics hold up better than MK64... Crazy challenges (as far as my under-10 year old self recalls) that kept me glued to the screen for the infinite hours my mother would spend walking the aisles. Honestly, I don't know if this game is any good now - and I'm going to have to track down a copy on eBay (surely it can't be much) - and it's not one I hear a lot about... but it is about *the* game I think of when I think Game Boy (mostly because I've played Link's Awakening on six systems that aren't the Game Boy... like, there's not a doubt in my mind that it's a GB title... there's just sooo much packed into it that it doesn't seem like one.

What individual titles define a particular system for you?