Ferrothorn is a large metallic Pokémon with a saucer-shaped body covered in green spines. It somewhat resembles a flattened durian fruit. Its metallic body is covered in sharp green thorns. It has three black stripes encircling its body; the middle stripe located below its eyes, is triangular. Its eyes have green rims, yellow scleras, and black pupils. There is a green spike at the top of its head. Long, thin green vine-like appendages tipped with spiky metal disks extend around it. Ferrothorn uses these spiny metal appendages to cling to ceilings of its cave habitat, or walk by slowly shuffling.
Much like its previous form, touching any of Ferrothorn's spiked barbs by accident when trying to pet it in the Pokémon-Amie will injure the player character's hand. This can make it rather tricky to raise its affection.
Ferrothorn appears to be based on a durian or a cocklebur, mixed with a mace.
Ferrothorn's name is derived from the Latin word "ferrum" meaning "iron" and the word "thorn".