Big Arm has two phases. On its first phase, it attempts to crush Sonic with its hands and use its rockets to dash. Once Big Arm has received four hits, it will advance to Phase 2, growing spikes on its arms. In this phase, Big Arm attempts to grab Sonic and throw him or punch Sonic from the edges and center of the arena. Big Arm is defeated after eight hits.
- 1-Ring Boss: Defeat Big Arm in 3:00:00 with 1 ring!
- On the original E3 demo, Big Arm had a remix of the Doomsday Zone theme, but it was changed by Gamescom to the correct remix.
- The remix features guitar solos that are highly reminiscent of themes from Sonic Adventure and Sonic Adventure 2.
- This was the very first boss stage that Sega confirmed would appear in Sonic Generations.
- Big Arm takes twice the amount of hits the Death Egg Robot can.
- Big Arm is the only boss in the Nintendo 3DS version of Sonic Generations that, on its original version, Sonic truly fought on his own. Sonic faced the Biolizard along with Shadow when it was in its final form, and he faced the Egg Emperor with Tails and Knuckles.
- This is the only stage in Sonic Generations that directly references Sonic 3.
- Interestingly, in Sonic 3 & Knuckles, the player had to go through Launch Base Zone in order to access Mushroom Hill Zone, but in Sonic Generations, it's the other way around (though Big Arm is not present in S3&K while playing as Sonic).
- Oddly, Classic Eggman is blacked out in the level select screen and the cutscene, but he is visible in the boss fight if you increase the brightness to 5.