In development since 2010, Halo: Out With a Whimper is a fan-made project looking to take the franchise’s frantic 3D gameplay and transfer it to the world of 2D platformers.
Going a little beyond your standard demake—of which there’s been plenty of Halo offerings previously—this is going all out, promising a “story driven campaign”, “the survival mode Firefight” and even stuff like armour customisation and stat tracking.
https://kotaku.com/inevitably-the-8-bit-halo-de-make-lands-in-january-5716550
You can check out more about the project, which hopes to be playable sometime “this Winter”, below.
Halo: Out With a Whimper [IndieDB]