Security Robot B.O.X.

The BOX is a boss in Metroid Fusion for two battles and is notable as being the only boss not infected by the X Parasites (in the first encounter)>

The box is a rogue security robot that first attacks Samus by ramming at her and launching bombs that create walls of fire moving in two directions. The only way to damage it is to get right above it and shoot power beam shots and missles down into it's core. Before it retreats, the player may notice that the now armorless core contains a human brain.

Later in the game, Samus' computer reveals that it'a organic parts have become infected by the X and is running rampent in the night region. In this battle the BOX fights in a shallow pool of water which is electrified as long as it is in contact with it (due to the X-core infecting it has Samus' wave beam) as well as shooting homeing missles at Samus. Despite it's weak spot being the same, it can now jump high enough to knock Samus off of the railing. Upon defeating BOX the brain changes into a hard X-core, defeating it returns Samus her wave beam.