T-5001's Neuron is a single brain cell (or neuron, as it were) that detached itself from T-5001's Brain after the T-5001 travelled backwards in time to create the UnWorld. Paradoxically, the neuron was the precursor to the T-5001's original form, the T-5000. It served as the primary antagonist of Mario's Adventure 4.
In the post-apocalyptic dystopia of the Neotubby Empire, the T-5001 transforms into its Final Form: a planet-sized robot that can shapeshift into an actual planet. Sensing that the end of the UnUniverse is approaching, the T-5001 travels back in time to before the UnWorld is created and physically becomes the UnWorld itself. Later, as the continents and seas form on its body, the T-5001 sends a single neuron onto its surface. There, the T-5001's Neuron adapts to its surrounding environment, shape-shifting into the T-5000. Thus, the cycle of the T-5001's life is complete.
In Mario's Adventure 4
In Mario's Adventure 4, T-5001's Neuron serves as the primary antagonist and the last remains of T-5001's Brain. It uses its ability to copy and possess other beings, including Weegee and Death incarnate, to fight the T-2500.5 in its upgraded T-2504 form. In doing so, it fights Death itself and loses its Undefeatable privileges, becoming vulnerable and subsequently dying.
Becoming an Independent Being
After the T-5001's Brain was defeated and sent back in time at the end of Mario's Adventure, it grew into what would later become the UnWorld itself. However, when it was sent back in time, it was not fully defeated, nor was it in top condition. No, it was wounded, and the tiny planetoid that was left of it was the very core of the T-5001's brain. In addition to this core, unbeknownst to anyone else, a single neuron remaining from the T-5001's brain was resting on the planetoid's surface. As the planetoid grew into a full-fledged planet, this single neuron lay at its core, biding its time and waiting for its nemesis, the T-2504, to reappear once again.
It survived lava and a thousand tons of pressure at the planet's core. It survived the shifting of the tectonic plates. It survived the mass extinction of the Worms brought upon them by the rage-filled hand of Chuck Norris. All it was doing was waiting underground, sensing the presence of anyone who walked by. When it sensed the footsteps of the T-2500.5, it popped out of the ground to meet him. Thus, the two enemies met once more.
Although T-5001's Neuron cannot shapeshift the way its predecessors could, it can copy the abilities and appearances of others, as well as possess them by fusing with their brain. For instance, it temporarily turned into an exact doppelganger of the T-2500.5, but it lost this appearance when the T-2500.5 hit it with a rocket-propelled grenade. Later, it dropped into the Cauldron of Evil, where it possessed Weegee's corpse and became the W-5001. This particular form is especially strong, as it has both the Weegee Stare and the invulnerability of T-5001's Neuron.
Restoring Its True Form
After a long and arduous battle with the T-2500.5, T-5001's Neuron found its way into Nintendo's headquarters and used Shigeru Miyamoto's personal Revival Machine. The T-2500.5 tried to erase history and kill T-5001's Neuron before it could enter the machine, but its efforts turned out to be futile. Now, the original T-5001 is on the hunt for the T-2500.5 (now upgraded to the T-2501) once again.
The T-5001's Neuron is a floating, green neuron that looks like a branch or vine. It glows whenever it copies the appearance of somebody else, just like the T-5001 and T-5001's Brain were able to.
- Telepathy (only used for communication)
- Telekinesis (limited to hovering)
- Copying the appearance of others
- Possessing others by taking control of their brain
- W-5001: A possessed version of Weegee, capable of hovering in midair.
- T-5001: The original form of T-5001's Neuron, restored by the Revival Machine.
- T-5001's Soul: A combination of Death and a walking fish. This form was all that remained of the T-5001's Neuron once it was "defeated".
When the T-5001's Neuron was turned into the T-5001's Soul, it was sent to the 37th Dead World, where it battled Death itself and copied part of its data, gaining a skeletal appearance. It managed to kill Death (how does that work?), but it was stripped of its rank as an Undefeatable. Since it could now be defeated, the T-2501 did just that. Now, it is dead. Very dead.