The Octabrain is an enemy in Duke Nukem Forever.
The Octabrain is a floating, medium-sized, octopus-shaped alien with three glowing eyes. One of its attacks consists of it tossing junk scattered throughout levels, such as barrels, at the player. It is also able to fire projectiles at the player from its brain. When stuck with a laser tripmine it will spin extremly fast and go kamikaze, trying to catch you in both the laser tripmine explosion and its own death-throes explosion.
Its deadliest ability is that it can catch any projectiles fired at it by the player and toss them back, such as Pipebombs and rockets. The pre-release podcast has revealed that this will be exploited in at least one boss battle, where Octabrains will appear and will catch any projectiles that are fired at the boss. It kinda looks like he does not have skin on his head, so it shows his brain, but this appears to not be confirmed yet.
The Octobrain flies around while attacking via 2 methods. The first is to hover in the air and fire an energy blast at your location. Shooting the Octabrain while it readies the shot will disrupt it from firing. The second attack is to levitate and throw objects in the surrounding environment at the player. This occurs quite quickly, but this typically occurs when there is significant cover as well.
Upon death the Octabrain's body will fall and explode, dealing damage to everything around its corpse upon detonation. This will occur even if frozen, as the falling body will explode before a shatter may be possible (not sure if it is possible). This will not occur if the Octabrain is shrunk and stepped on, which is an effective weapon against them.
RPGs and Devastator shots fired around the Octabrain will be thrown back at the player, and it is unadvised to use those weapons. Pipe bombs will also be thrown back at the player, but enough time is given to detonate it before this occurs. Combined with the nature of catching projectiles, pipe bombs are an effective weapon due to the Octabrain pulling the pipebomb close.