Magneton in depth
Rarecoil, or the chrome that isn't there
Its Japanese name is レアコイル, “Rare Coil”: “rare”, meaning uncommon or scarce, attached to コイル, the Japanese name for Magnemite. The joke is aimed at collectors—the common chrome and the rare chrome from the same series. English, and Spanish along with it, takes a different route, combining “magnet” with the “-ton” suffix, following the pattern already established by Magnemite.
The design explains itself: three Magnemite joined by magnetism. In the games where it can be seen moving in three dimensions, the three units move independently without breaking the triangle. And there is a crack in the species' own logic, because one official description admits that a Magnemite can evolve on its own when there are no others nearby. Three bodies that aren't always three.
The day it stopped being only Electric
In Generation I it was pure Electric, and its Special was a single value of 120 that worked equally well for dealing and taking damage. Generation II did two things at once: split that stat into 120 Special Attack and 70 Special Defense, and added the Steel type, which had just been introduced. The result was a huge gain in resistances and an immunity to Poison, in exchange for becoming vulnerable to Fire and Fighting, which had previously treated it normally.
The Ability that defines it today didn't even exist at the time: Magnet Pull arrived in Generation III. And in Generation IX it lost the effect it had outside battle, when it could attract Steel-types to wild encounters.
Three bodies, one gap in the line
It shares an idea with Dugtrio that Generation I used twice without even trying to hide it: take a small creature and multiply it by three without changing anything else. The difference is what happened afterwards. Dugtrio remained a final evolution; Generation IV put Magnezone above Magneton and pushed it into the middle of the line, the worst possible place for a Pokémon whose only good number is Special Attack.
That leaves players with a specific decision: with a Thunder Stone or a magnetic field readily available, staying as Magneton only makes sense if you plan to take advantage of Eviolite, and there are few points in a playthrough where that pays off.
What to send it out against—and what not to
Its best role is predictable and it works: bring it in against Flying- and Water-types, let it resist whatever they throw at it, and answer with Spark. Against Steel, Magnet Pull traps the target, though it's worth checking which Steel-type it is—Excadrill can't escape, yes, and still wins the exchange because it hits with Ground.
That's where the less well-known trick in its level-up list comes in. Magnet Rise, at 28, lifts it off the ground and removes the weakness that actually kills it for a few turns. Almost nobody teaches it the move, but it completely changes what a Ground-type opponent can do when it expected to settle the matter in one hit.
The rest of its movepool is flatter than it looks. Screech at 24 and Lock-On at 58 are status moves that rarely justify the turn, Metal Sound at 46 lowers the opposing Pokémon's Special Defense but requires staying on the field with 50 HP, and Light Screen at 52 arrives too late to be much use. Its strangest card, Tri Attack, is learned at level 0 and is Normal-type, with no STAB, and 80 power. A Pokémon built around a single good number, forgiven for everything else because that number is 120.