Swampert is an amphibian-like Pokémon with a bulky frame and four thick limbs, the two longer ones at the front serving as arms while the shorter limbs provide support for the creature if it chooses to stand upright. Swampert is semi-bipedal. It can stand on its three-toed feet with a hunched posture, and pick up or grab objects with its hands, but when moving about it tends to run on all four limbs. It has orange conical gills that protrude from round patches on either side of its face. Two large fan-like black fins extend from the top of its orange eyes to the back of its head. Similarly, a black fan-like tail fin extends upward from its hindquarters. Swampert is predominantly cobalt with a white abdomen, orange gills, and similarly orange padding on all four limbs.
Swampert boasts the physical strength to easily drag a boulder weighing more than a ton, batter down opponents, and swim faster than a jet ski. It has keen eyesight, enabling it to see in murky waters. Swampert also has the ability to predict storms, sensing subtle differences in the sounds of waves and tidal winds with its fins. When a storm is approaching, Swampert will pile up boulders to protect its nest. It makes its nests on beautiful beaches. The reason Swampert covers itself in mud is that it wants to keep its skin moist. In Generation III, Muddy Water was its signature move.
As Mega Swampert, this Pokémon gains considerable bulk. Its upper body and arms become more muscular, bulging compared to its squat lower body. The orange padding on Swampert's thighs vanish, but it gains two additional patches of orange padding on each wrist and another patch on each shoulder. This padding and its gills become a darker, redder shade of orange, while the gills are now larger and bulbous, with filaments extending past its mouth. The black fins on its head are thicker and now extend down past its shoulders. The black tail fin is still shaped like an upward-turned fan, but it now forms a short ridge that extends up to this Pokémon's forehead, flanked on either side by the aforementioned head-fins. The webbed digits on Mega Swampert's "hands" take on a black color and now feature better defined articulations. According to the anime, Mega Swampert fills the organs on its back with air before diving underwater or battling; it uses that pressure to increase the power of its punches.
Swampert debuted in Abandon Ship!, where Tommy's Marshtomp was revealed to have evolved into one while living in the Forsaken Ship ever since it was accidentally separated from Tommy. Since then, it had come to believe that Tommy had abandoned it. When Ash and his friends arrived on the Forsaken Ship and ran into Tommy, Swampert abducted them one by one and trapped them in the webbing of its Spinarak partner until only Ash, Brock, Tommy, and Pikachu were left. After Swampert's memory was rehabilitated, the two officially reunited.
Swampert, the Mud Fish Pokémon. Swampert is the evolved form of Marshtomp. It is able to easily drag large stone weighing over one ton. It is also able to see through cloudy waters and detect approaching storms with its fin.
Swampert has the highest base stat total of any fully-evolved starter Pokémon.
Mega Swampert is the only Pokémon with a base stat total of 635.
Swampert and its pre-evolved form are the only starter Pokémon to have a 4× weakness against another starter type.
Like its pre-evolved forms, Swampert appears to be based on the mudpuppy, axolotl, mudskipper, or the gilled African lungfish. Swampert's portrayal in the anime suggests that it could also be based on common depictions of a swamp monster—a fictional, frequently antagonistic creature imagined to live in swamps and often has some physical humanoid traits. The fins on its head and tail resemble Japanese war fans, also known as tessen. Its stance is reminiscent of sumo wrestlers.
Swampert may be a combination of swamp and rampart, expert, or earth.
Laglarge may be a combination of lagoon, large, and possibly lag or lug.