A few days ago, one Spanish user of 4Chan’s /v/, who had gotten ahold of a review copy of the Nintendo 3DS version of Sonic Lost World, decided to reveal many major details about the game, including the storyline, a few screenshots, and... the final boss.
According to this source, Eggman gains control of the Deadly Six using a conch shell (called the Cacophonic Conch in the Archie adaptation,) by the way. Then, after Sonic gets rid of the shell, as we've already seen, Eggman and Sonic must team up to stop the Deadly Six from using Eggman's badniks for their own evil means. This conflict ends in the defeat of the Zeti... and the betrayal of Eggman.
Like we didn't see that coming.
Lava Mountain's zones don't appear at all in the 3DS version of Sonic Lost World. Instead, the player must fight his or her way through a boss rush, which includes every boss encountered in the game and ends in a fight with one of Eggman's giant robots. The leaker also pointed out that the Deadly Six's boss battles are quite short, and that the Deadly Six are barely present in the game. However, he notes that it takes about seven hours to complete the game.
Wanna see the final boss? Here you go!
Thanks to ModrenSonic for uploading the screenshots, and thanks to TSSZ News for reporting it!