This is actually a landmark occasion in the SEGA and Nintendo partnership as it marks the first time Sonic has appeared in a official, traditional Mario/Yoshi style level. As you can see in the video and images, many of the enemies you’ve come to know playing through Mario games are present, as well as Sonic’s traditional loops. It’s like a Sonic/Mario/Yoshi mash-up level, and that’s actually incredibly awesome.
According to SEGA’s post, Sonic must help Yoshi find all his missing eggs, which are hidden throughout the level. Sounds like a fun time, especially if you’ve played through the game already. James played through Lost World for his review, and he seemed to like it quite a bit. I wonder what he’d think of this new DLC, though!