Big Arm is a heavily armored, egg-shaped Egg Mobile. Significantly modified compared to the regular Egg Mobile, it possesses two big, mechanical arms on the sides. These arms are gray with red shoulder disks, wrists, finger surfaces, and knuckles. It also possesses a windshield and a red canopy with gray spikes on it. It has also two small red thrusters on its back and retractable spikes on its forearms.
Powers and abilities
Big Arm is able to hover or fly through the air using the thrusters on its back. Its arms also give this vehicle the ability to grab its opponents and throw them into the ground with lethal force, make powerful palm thrusts, and throw tremor-inducing punches.
During the first phase of the battle, Big Arms mostly attacks by aiming and launching its punch at the player. However, it is easy to avoid getting hit by it. By the time it is launching its fist, it will lower its cockpit, giving the player the opportunity to hit the downward part of its cockpit twice; one before it embarks its punch attack, and another after the punch is embarked. If the player fails to use these opportunities to deliver an attack on it, Big Arm will land aground and use its rocket to dash and hurt the player from the left to right and vice versa. After that, the Big Arm will return immediately to smack the player with its fist.
After four percents of its Health Gauge are depleted, Big Arm will change its pattern of attacks, initiating the second phase of the battle. Firstly, it protrudes spikes on its arms and will try to punch Sonic from the edges and center of the arena. After that, it will appear from one of the sides and attempt to catch and toss Sonic into the ground, causing the player to lose Rings. When this happens, the player has to jump to the other side behind Big Arm and move quickly toward it to damage the lower part of the cockpit using the Spin Attack. Continue using this opportunity to attack Big Arm will help the player finish the battle.
It takes eight hits to defeat Big Arm.
1-Ring Boss: Defeat Big Arm in 3:00:00 with 1 ring!
While battling this boss, the music was originally going to be a rock remix of the theme heard in the The Doomsday Zone. This remix was only used in the E3 2011 version of the demo, as in the Gamescom 2011 demo it was replaced by a remix of its original theme; the final boss theme from Sonic the Hedgehog 3.
This is the only boss from Sonic the Hedgehog 3 to appear in Sonic Generations. Likewise, its Launch Base arena is the only level from Sonic the Hedgehog 3 to appear in Sonic Generations, as both versions take their main levels from Sonic & Knuckles.
Big Arm was the very first boss that Sega confirmed would appear in Sonic Generations.
Big Arm takes twice the amount of hits that the Death Egg Robot needs to be defeated.
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 with Shadow when it was in its final form, and he faced the Egg Emperor with Tails and Knuckles.
Oddly, Dr. 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.
There is a glitch where Big Arm will be stuck charging up his punch; it will still follow the player around, and it will play the charging up animation, but it will never bring the punch down, and it is too high to be hit, as shown here and here. The only solution is to exit the battle.