Big Icedus (ビッグアイスダス,Biggua Isudasu?) is a sub-boss in Sonic the Hedgehog 3 that the player will encounter ar the end of IceCap Zone Act 1. It takes six hits to defeat it.
Created by Dr. Robotnik, Big Icedus is floating frosty machine that floats around the arena with eight snow blocks guarding it. It has a grey main body and three magnetic ends on the body's sides and bottom. It also has what it looks like two eyes and mouth.
After getting out the cavern of IceCap Zone to the cold external weather, the player encounters the Big Icedus which flies down into the arena. It then summons eight ice blocks from the snowy grounds which it uses as shield and swoops down in a U shape across the screen once or twice. It will then launch the ice blocks into the air, where they will eventually fall down to the ground. Depending where the Big Icedus is standing, three ice blocks will usually fall to the left side and two others will fall to the right side. The player cannot destroy the ice blocks and will only take damaged when touching them. After this, Big Icedus will repeat its pattern again.
During the fight, the Big Icedus will be too high to reach at first. The best chance to hit Big Icedus is after it throws up its ice blocks, as it is at this point where it is at its lowest height. However, the player also has can the chance to hit it normally by using the Lightning Shield as Sonic at the right time or flying as Tails. After six hits, the Big icedus gets destroyed and the background gets more brighter than before.
In locked-on version of Sonic the Hedgehog 3 & Knuckles, Knuckles will go through his own pathway to the lower part of IceCap Zone Act 1 and faces the Big Icedus in a huge cavern. The battle is the same, except due the Knuckles' low jump height, the battle may take little longer.