For A Few Dogs More
I took part in a game jam recently, in which I used HaxeFlixel. The theme of the jam was "the wild west", so I made For A Few Dogs More, a game where you play as two dogs (a wolf and a prairie dog) riding from town to town, shooting critters and jumping over obstacles. The wolf and dog are controlled separately, a la the Mario and Luigi games, so you can play with a friend (both on keyboard, or one on gamepad one on keyboard), or solo, which can be challenging.
Bear in mind, this game was made for a two day jam, so there are a lot of things I wanted to add that I didn't get around to yet (such as support for two controllers).
Nice font for the Title and Game Over. The Sprites for the dogs are quite nice too.
I don't know what kind of Mario and Luigi games you talk about, so this is quite a new gameplay to me. I really liked it.
Managed to complete alone on my keyboard.
I'm referring to the handheld RPG series, where you play as both at the same time, and they each have individual jump/action buttons. I suppose there's a bit of a Mario/Yoshi from Super Mario World dynamic to it, too.