Big Arm is a boss battle in the 3DS version of Sonic Generations. It is the boss of the Classic era and is a remake of the final boss battle from Sonic the Hedgehog 3.
Big Arm has 2 phases. The 1st phase has him trying to crush you. The 2nd phase has him having spikes on his arms and trying to grab you.
1-Ring Boss: Defeat Big Arm in 3:00 with 1 Ring!