Goodra is a pudgy bipedal Dragon-type Pokémon that is coated and dripping with goo. Its ventral portion is mauve, while its dorsal side is lavender. It has bright green eyes, and two green spots on either side of its face and three on either side of its thick tail which curls inward. Goodra have two sets of antennae atop their head that are capable of retracting. The front pair of antennae are short, skinny and stand upright, while the back pair are long and thick, drooping downward behind its head and curling upward toward their tapering ends. They are very dextrous and can be used for grabbing onto things, and can be extended to almost 3 times Goodra's height, as seen in the anime. A pale green slime drips from Goodra's chin and arms.
Goodra is capable of throwing very strong punches. It is very affectionate and, when it hugs its Trainer, leaves them covered in goo. Goodra is easily overcome by loneliness though, and oozes gooey tears when left to itself. Although it gets teased because of its meek nature, it fights back with powerful horn and tail attacks. Its slimy skin and thick fat layer allows it to brush off enemy attacks with ease.
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.