This is Super Time Force by Capybara Games, and while retro-graphics platformers and rewind-time mechanics are not new concepts, what the studio is doing here with both looks new and cool as all hell to me.
As the Capy representative explains to Stephen Totilo, when your character dies in the game, you'll be given the opportunity to go back in time, spawn as a new class of fighter and fighting alongside that past self, save him from whatever threat it was that killed him. Ultimate failure is simply running out of lives. Other than that, you can have as many as 499 of your past selves fighting alongside your current character on the screen, claims Capybara.
Really. This "pet project" of the studio, which it hopes to release in late 2012 or early 2013, has seen 500 characters on the screen at the same time. And that's where the low-res graphics come in handy, as rendering that many in that style doesn't slow down the Xbox 360.