OK, Reddit user Bearskopff has uploaded an image of a level he created in Halo 5 Forge to Reddit VIA Imgur.
"I was feeling nostalgic so decided to try and recreate the infamous castle from Super Mario 64 in Halo 5 Forge. Had quite a bit of fun and as many headaches trying to piece it all together but am pretty pleased with the final result - hope you are too! My GT is 'Bearskopff' so feel free to download it, add a few game mechanics and give it a play. Enjoy :)"~BearskopffOf course he's left out some elements like the waterfall and stained glass windows. But we've gotta give him credit for trying so hard. He did a good job, and it must've taken a while to create a level with such similarities to the original game.
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Remember, Mario-Time-all-the-time