- "Based on a dream Porky once had. 'N.K.' stands for 'Natural Killer.'"
- — Battle Memory
The Natural Killer Cyborg (N.K. Cyborg for short) is a boss in Mother 3. It is a giant robot used to guard the entrance to Porky Minch's lair on the 100th floor of the Empire Porky Building. It bears some resemblence to Einswines, though it is set apart by its large red eyes, spider-like legs, and black pincers.
The Natural Killer Cyborg is the strongest enemy encountered in Mother 3, and proportionately gives the most EXP upon defeat. Technically, the King Statue is stronger based on raw stats; however, it has fatal weaknesses to the New Year's Eve Bomb and PK Flash, whereas the N.K. Cyborg has no such vulnerability. The N.K. Cyborg's sprite is also the largest in the game, even being the only one too large to properly fit in the Battle Memory; however, this does not make it the largest enemy, as the King Statue is depicted as an actual monument towering over the party in the overworld, and it is argued that the statue's battle sprite was scaled down.
The Natural Killer Cyborg has a large array of powerful attacks at its disposal, made deadlier by its ability to sometimes attack twice in one turn. Like other strong enemies, it can take a powerful swing, which damages one target and may inflict forgetfulness. It can also bear down and attack, dealing massive damage to a single target. It is not restricted to attacking one target at a time, however; it can fire several missiles at three random targets, and it can hit the entire party with poisonous gas or an electric shock attack. The electric shock is its only PSI-based attack, but due to being Thunder-element, it bypasses PSI Shields and Counters; however, if it targets Lucas, the Franklin Badge will reflect that portion of the attack back at the N.K. Cyborg. To defend itself, it can use a Counter device or a PSI Counter device, and it can activate its Self-Repair System to restore over 500 HP.
Its signature attack is the End of the Century Beam: it uses reticles to take aim at every party member who isn't incapacitated, then it changes its sprite to reveal a cannon in its mouth, from which it fires a massive rainbow-colored beam to deal high damage to the entire party. Despite being a beam attack, its damage is oddly counted as physical. It is possible to defeat the N.K. Cyborg before it uses this attack with a well-timed PK Ground, but this is not recommended, as letting it use the attack is required to complete the Battle Memory.
Counters go a long way in making the Natural Killer Cyborg more manageable; Offense Down and the Scary Mask are also highly recommended. The Shield Snatcher naturally comes in handy when it sets up its Counter. Aside from that, it is recommended to go all-out with the most powerful attacks at the party's disposal, since an Instant Revitalizing Machine can be found and used before the next fight. If Kumatora is at a high-enough level to know it, PK Ground will defeat the N.K. Cyborg in three or four turns, like any single enemy.
His battle sound is Battle Sound 60, a battle sound used only by large bosses, which falls under Code Numbers 939 for regular attack, 940 for Smaaaash! and 941 for Miss.
- Due to the fact that the original version of Mother 3, EarthBound 64, was going to come out in 1999 for the Nintendo 64, the End of the Century beam may have been a play on the new century approaching.
- A Natural Killer (NK) is an immunity cell.
- N.K. Cyborg's battle theme sounds very similar to Beat It by Michael Jackson, and also the Dr. Wily stage theme from Mega Man 2.