Italic movea get STAB only when used by an evolution of Nupin
Underlined moves are unavailable to a prior evolution(s) and/or will be completely unavailable upon evolving.
By breeding
Nupin is genderless, it can't get any of the Egg Moves listed through natural means (unless learnable elsewhere such as via a Mystery Gift event, TM, and/or Move Tutor).
Nupin and Gellin were designed by Involuntary Twitch for an old project of hers called Pokémon Amber along with the Sheebit line. They are some of Twitch's oldest fakemon designs.
In earlier versions, Nupin was a slug-like Pokémon with no eyes. This resembles real life single-celled organisms more, most of whom don't have eyes.
No other Pokémon has the same type combination as Nuclear Nupin and its evolution.
By extension, Nuclear Nupin and its evolution are the only Grass types paired with the Nuclear type.
Design origin
Nupin is based off of a single-celled organism, possibly an amoeba or a bacteria. It may also derive from phytoplankton, considering its Grass typing and photosynthetic abilities.
Name Origin
Nupin may be a combination of Nuppi (Finnish for button), Nupa (Javanese for mushroom) and pin.