The Halo 2 Arbiter mission that Bungie scrapped 21 years ago has been officially restored as a playable Master Chief Collection mod

gamesradar.com:

A Halo 2 level that was scrapped well before its 2004 release has now been officially excavated, dusted off, and made playable within The Master Chief Collection. 

Halo Studios and modders The Digsite Team have been restoring lost Halo content for years now, starting off with never-before-seen maps and weapons and vehicles that original series developer Bungie left on the cutting room floor. It's fitting for a series all about exploring ancient, long abandoned alien structures, but Digsite have recently gotten even more ambitious with its goal.

For Halo 2's massive 20th anniversary, the team went back to the game's infamous E3 2003 demo that never made it into the full game, spruced it up with existing assets and all-new ones, and then released it as a mod for Halo: The Master Chief Collection's PC version. They've now done the same with a long-lost Arbiter mission that sent humanity's alien bestie to a desolate moon impaled with the shards of the titular Halo from the first game.

"This scenario is a composite reconstruction of the 2003 mission '05_alphamoon' assembled from archived data, design documents, and our own restorative work to showcase early Halo 2 development," the mission's start-up screen reads. "While care has been taken to present this level in a further completed state, Alpha Moon originally never developed beyond the 'Halo 1.5' phase." As such, you might bump into some unintended bugs or difficulty hikes.

That's a small price to pay for another classic Halo campaign level, though. Alpha Moon follows a formula that the series has used over and over for a reason. It starts out lowkey with the Arbiter touching down on his lonesome, equipped with nothing other than a rifle and an invisibility power-up for some stealthy back melees. But it doesn't take long for those explosions (and explosive guitar riffs) to come in as the level soon puts you into a Covenant tank where, in classic Halo fashion, you're blasting an outdoor corridor full of little grunt