You found a Wartortle!
Wartortle (カメール Kamēru, Kameil), known as the Turtle Pokémon, is the evolved form of Squirtle. It has a slightly more intimidating appearance than its preceding form; aside from an increased height and weight, it now has darker skin, eyes with smaller pupils, and two protruding fangs. Its shell may receive scars from battles that these Pokémon seek out. A Wartortle also gets a pair of feathery ears, and its tail becomes white, fluffy, and too long to completely hide within its shell; these appendages greatly aid this Pokémon in swimming, acting as oars and/or fins. The tail also happens to be a highly valued collectors’ item, which has caused people to hunt this Pokémon, dwindling their numbers. The reason for such poaching may very well be that a Wartortle tail is a symbol of longevity in the Pokémon world, supposedly allowing the creature to live for thousands of years.
In the anime, the first appearance of a Wartortle is when a wild one runs into Ash Ketchum and his friends on Cinnabar Island, seeking help for its clan of Squirtle, Wartortle, and a leading Blastoise, all mysteriously stricken with sleepiness. More Wartortle appear as firefighting Pokémon, and Ash’s Squirtle, being an honorary firefighter of its hometown, forms a rivalry with the leader.
GamesRadar editor Brett Elston compared it to Ivysaur and Charmeleon, describing it as a pit stop to a more powerful Pokémon.