Part 0: Codi
Trailhead the First
On 2016-03-17, a post appeared on /r/gamedetectives saying that Teragon Group's website had changed. Six hours later, Discord user VintageKeith checked the page and found that it was hacked by an entity named Codi.
Four hours later, the site reverted to its usual look.
The next day this video appeared on the channel, with the description saying it was "sponsored by Codi". The game shown in the video is *Stardew Valley*, and this channel was discovered through this hint.
A Warm Welcome
The video Hi There drew attention as it was the newest one and different to the others. The text said:
Hi there. My name is Codi. Do you want to know me? Let’s see if you're smart enough. Solve this riddle. [Mirrored] See you on the other side.
The video itself is flashing images of asterisks.
The first video is the Star Spangled Banner (American national anthem), and the second one is Twinkle Twinkle.