While the Mario series I'm the biggest fan of (I mean as a whole not just the platforming), I'm also a seasoned Pokemon player and I've played extensively Pokemon Sapphire, Pokemon LeafGreen Pokemon Pearl, Pokemon HeartGold (my last main game I played a lot since I was getting burnt by then) and a bit of Pokemon Black (or White, don't remember). I also played Blue Rescue Team to death, played Explorers of Time which I didn't like as much, and played Super Mystery Dungeon, generally the post-game. While I'm a sucker for Mario merch, I'm a big sucker for Pokemon merchandise too. I gotten in to Pokemon at a very young age, playing Pokemon Blue a lot and not really knowing what I'm doing, so Gen 3's the one that really got me in.
I also enjoy Yo-Kai Watch a lot, got hooked, but after I stopped, got lazy and didn't end up progressing past a certain point. I prefer Pokemon designs in general, as Yo-Kai creatures are far less cute, but I do have some Yo-Kai I like a lot like the Cicada, the D'wanna thing, the sad bird thing, the laughing eel thing, but there's no merch of it compared to the Jibanyay cruft, so I dislike Jibanyan probably even more than Pikachu. My friend gifted me it, so I decided to play it.
I also played several Rayman games. I dabbled a bit in Rayman 2 (in the 3DS, though probably not the best iteration of it compared to, say, Rayman Revolution) and Rayman 3. Rayman Origins and Rayman Legends are among my favorite 2D platformers of all time. I knew Rayman mainly from Rayman 2 that my brother played. Rayman Origins was a game we weren't exactly screaming and running to get since it was virtually unknown and not talked about, but we heard great things about it (and on these boards years ago iirc), being comparable to New Super Mario Bros. Wii. We played Origins and we instantly fell in love with it, and it made us sometimes realize what Mario games can learn from. Because of Origins, I really want Rayman as a playable character in Smash Bros..
Super Smash Bros. is one of my childhood games. I got in to it long before I remember why. I know it made me recognize all the Nintendo characters, and I believe it's the thing that kickstarted my gaming life. Anyway, I got and played tons of hours in every Smash Bros. to date. Brawl's my least favorite in the series.
Left 4 Dead, my sister already talked about it. My friend shared us a video of silly Mario mods in Left 4 Dead, and the ridiculous voice acting hooked me in, as well as existing mods for playable Mario (from Super Mario 64).
Grand Theft Auto: Played only GTA V, but I love it. It's a lot better with mods on, and I modded in Mario and let him either stroll peacefully or wreak havoc while the graffiti's a bunch of random stuff from our life.
I also sunk way too many hours on Spore and its expansion: Spore Galactic Adventure. I wasn't part of the hype crowd, only I heard about a super flexible evolution sim and decided to check it out. One of our first PC games, and it's before the advent of online gaming store fronts, at least for me since I didn't have a Steam account. I just love the Galactic Adventures part of it so much, and the mods make it so much better, making up for the stark lack of content for it after its release.
Edit: I forgot to mention I'm an avid fan of the Kirby games. I've played (copy pasted) Amazing Mirror, Air Ride, Canvas Curse, Mass Attack, Squeak Squad, Return to Dream Land, Epic Yarn, Nightmare in Dream Land, Star Allies, Triple Deluxe, Superstar Ultra, Kirby Fighters Deluxe, and I have Kirby's Dream Collection. I'm still wanting a plushie of the Yellow Kirby as that's my favorite color of Kirby.