This is the oddest beasts I’ve tackled so far. There’s plenty of Fantastic Beasts and Dungeons & Dragons monsters that have the same name/origins. So far, they’ve been different enough to make the creation of their game stats interesting.
A Gnome is not a beast or monster in D&D though. No, a Gnome is a playable race, with their own history, culture and intelligence.
Suggesting that a D&D Gnome was a small pest that infests gardens, steals vegetables and occasionally bites ankles would be extremely racist.
So, right off the bat, the Potterverse gnome is now a ‘Gernumbli’. Apparently an alternative name for Gnomes in this fantasy world is Gernumbli Gardensi, so we’ll lean on that. I don’t think ‘garden gnome’ separates these two creatures out far enough.
Gernumbli

The regular D&D gnome can raise to the rank of Level 20 wizard or ranger, saving the world from god-monsters. The Garden Gnome/Gernumbli is an idiot-pest that is not going to cause even a solo adventurer too much trouble. Especially if you include the Fantastic Beasts advice in your game mechanics: a Gernumbli can be dispatched by just spinning them round and round and chucking it.
Of course, if you are running a Harry Potter-based D&D game, you’re not going to need to be concerned about crossed wires. Goblins in the Potterverse are more culturally and socially comparable to the D&D gnomes than Gernumbli.
Thank You For Reading
From Acromantula to Gnome, you can find Dungeons & Dragons versions of other Fantastic Beasts here.