Goodra is a bipedal, draconic Pokémon that is coated with slime. Most of its body is pale purple with a darker purple underside. It has bright green eyes, two green spots on each cheek, a relatively long neck, and a short, rounded snout. On top of its head are two pairs of antenna-like horns. The foremost horns are small nubs, but the hind horns are longer, thicker, and curve down its neck. The tips of the larger horns are slightly curled. It has proportionally short limbs with two digits each and a large, thick tail with a curled tip. Along each side of its tail are three green spots. A pale green slime is usually visible dripping from its chin and arms.
Because of its meek, friendly nature, Goodra is often teased. However, it will strike at its tormentors with its retractable horns and powerful tail. It is also capable of throwing punches with incredible force. Its slimy coating in combination with a layer of fat causes attacks to slide off. When it grows close to someone, it will hug them and leave them coated in slime. If it is left alone, it will ooze gooey tears.
Goodra, due to its Dragon type, elongated body shape, and retractable tentacles used for battling is probably based on the Lou Carcolh, a mythical serpent/mollusk creature from French folklore.
Like its pre-evolutions, it could also be based on soft bodied gastropods, such as slugs and nudibranch; in particular, the "blue dragon" sea slug; Goodra's Pokédex entry may be a reference to slug's retractable eyes, which retract when they are in danger.
Alternatively, it could be based on the yōkai called Shussebora, meaning "ascended trumpet shell", which is a trumpet shell snail that lives 1000 years in the mountains, 1000 on the plains, and 1000 at sea, then will ascend and turn into a dragon.
Goodra is a combination of goo and dragon. It may also be a play on good or hydra.
Numelgon may be a combination of 滑る numeru (to be slippery), gel, and dragon.