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. It is known for having a great affinity for water, being able to live within water with no difficulty at all, as well as dive and surf all around the area.
Because of its meek, friendly nature, Goodra is often teased for supposed weakness. Goodra is known to be very friendly. 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 usually misunderstands instructions, appearing dazed or bewildered. Despite this, many Trainers don't mind it, instead finding this behavior to be adorable. However, it will strike at its tormentors with its retractable horns and powerful tail. Goodra can become uncontrollable once enraged. The horns can hit 100 times harder than the blow of a heavyweight boxer. 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. Goodra lives in plains and mountains, usually during rainy days.
Hisuian Goodra has droopy, gray eyes and horns that are longer and thinner than Kalosian Goodra's horns. It sports a large, spiral-shaped metallic shell on its back, which it can tuck its body into to protect itself, leaving only its head outside of the shell to observe its surroundings. It can control the hardness of its shell at will. It has fewer gray spots than Kalosian Goodra, with one on each side of its cheek and two on each side of its shell. From its chin and arms drips a metallic gray slime. Hisuian Goodra has a clingy disposition and hates being alone; it will become angry and run riot if its closest companions leave its side.
Goodra, due to its Dragon type, elongated body shape, and retractable tentacles used for battling is probably based on 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.
Hisuian Goodra is likely based on a snail. Its metallic shell in particular may be based on the scaly-foot gastropod, a species of deep-sea snail unique for its shell, which consists of iron sulfide compounds.
Goodra may be a combination of goo and dragon. It may also involve good or Hydra.
Numelgon may be a combination of 滑る numeru (to be slippery), gel, and dragon.