Cell BatteryMinun in depth
Two creatures made to sell a mechanic
Ruby and Sapphire introduced double battles, and this pair is the idea taken to its extreme: two creatures whose standard abilities do nothing unless the other one is on the field. In those games, both appeared on Route 110, and they stayed there in Omega Ruby and Alpha Sapphire. In Scarlet and Violet, they can be found in the Canyon Biome and the Polar Biome.
The fact that they were designed as a pair also explains the symmetry in their stats. Both add up to 405 and both reach 95 Speed, but Plusle distributes 50 Attack and 40 Defense against Minun's 40 and 50, and has 85 Special Attack against 75. It is the same Pokémon from two different angles.
The minus that gives it its name
マイナン is built from マイナス, the Japanese transcription of minus, with an ending that sounds diminutive; the English Minun does exactly the same thing with the original word, and Spanish kept the English name. プラスル, the one beside it, comes from plus by the same process. The sign is not just in the name: it is painted on their cheeks and defines which side of the circuit each one is on.
What kept changing
During the third and fourth generations, Minus only activated if the ally had Plus, and since Minun was the only Pokémon capable of having Minus at the time, that literally meant bringing a Plusle alongside it. The fifth generation loosened the requirement: from then on, an ally with Plus or Minus was enough, and the ability stopped being exclusive—Electrike and Manectric have it as a hidden ability, and the Klink line has it as a second option. The sixth gave it Volt Absorb, the best news it has received in twenty years. Its base experience also changed from 120 to 142 starting in the fifth generation.
It did not appear in Sword and Shield, which cost it an entire generation out of circulation.
Oddities in its movepool
At level 49 it learns Entrainment, which gives the target the user's ability. Used on the ally in a double battle, it gives that ally its own Minus and thus activates both abilities, a twisted way of meeting the ability's requirement without depending on which partner happens to be on the team. At 22 it has Copycat and at 13 Switcheroo, two moves that depend entirely on what the opponent does.
Compared with Pachirisu, the Electric rodent that arrived two generations later with the same 405 points and the same 95 Speed, Minun loses in physical bulk—70 Defense against 50—and gains in Special Attack. Neither of them breaks anything on its own.
In the anime, it debuted alongside Plusle on a lighthouse keeper's team. In Pokémon Adventures, it is part of Sapphire's team, where she uses it specifically to learn how to battle in doubles.