I have a confession to make: When I was young, I’d start two-player “Mario Bros.” games by myself so that I could play as Luigi. In “Super Mario Bros.,” I’d kill off Mario immediately so that I could control Player 2 and fly through the game’s eight worlds as his green palette swap. In “Super Mario Bros. 3,” there was something about a green Raccoon Suit that made my 5-year-old heart flutter. There was really no rhyme or reason to it. I just liked green a lot.

But those workarounds ended last week when Luigi finally got a side-scrolling platforming adventure all his own: “New Super Luigi U.”

For the first time in his 30 years playing second fiddle, the Eternal Understudy is finally in charge and it’s a beautiful thing. Serving as downloadable content for Wii U launch title “New Super Mario Bros. U,” this new game — currently available exclusively as a digital download through the WiiU eShop for $20 and later this year as a retail release for $30 — is a no-brainer for anyone who currently owns Nintendo’s newest console.

This title is not for the faint of heart. ”New Super Luigi U” distinguishes itself from its predecessor by taking the original 86 stages, imposing a 100-second time limit to each one and making most of them punishingly difficult.  I can’t remember the last time I finished a game in the “New Super Mario Bros.” series with fewer than 30 lives upon encountering Bowser for the final battle.

I ended this game with four.

In addition to grueling level design, “Luigi U” revives gameplay elements that have defined its protagonist since the American version of “Super Mario Bros. 2″ debuted in 1998. He jumps higher, lingers in the air and slides longer when changing direction while he’s running than Mario does. Although this is incredibly handy when it comes to finding the myriad secrets each stage offers, these new mechanics make it incredibly difficult to perform some of the tougher platforming segments in the game.

But that’s never a detriment to gameplay. If anything, it forces players to adapt to the nuances in Luigi’s mechanics. And once players finish the main story, they have the option of adopting the original “New Super Mario Bros. U” gameplay mechanics at the outset of each stage.

In addition to these gameplay tweaks, “New Super Luigi U” introduces Nabbit as a playable character. For those who haven’t played the original, Nabbit is a hooded rabbit who periodically appears throughout the course of “New Super Mario Bros. U,” stealing Toad’s loot and infiltrating stages. In “Luigi U,” Nabbit players cannot be harmed by enemies and, rather than powering up when he collects items, stashes them in his bag and dispenses them as 1ups at the end of the stage.

Although Luigi and Nabbit provide two excellent gameplay progressions, the two Toads who return from the original game play the same as they always have. This feels like a missed opportunity. What if Princess Peach joined in and added even more diversity to the gameplay?

Certain powerups that weren’t available in the “New Super Mario Bros. U” campaign also make a return, among those the Propellor Suit and the Penguin Suit. Don’t get too excited, though: Both of these powers fit into the theme of introducing variety in gameplay while simultaneously making stages incredibly difficult.

Nintendo’s approach in crafting “New Super Luigi U” echoes the various level editor projects fans have undertaken over the years. Level design defies the usual conventions Nintendo has applied in its “Mario” platformers over the years, with enemies popping up in unexpected places and several segments requiring incredibly specific timing.

Despite minor issues, this is a polished and well put-together title worthy of the “Super Mario Bros.” series. This is DLC done right.