Declime is a Water type Pokémon. Declime is No. 090 on the Pokédex. It is a sprite-swap of Shellder, and as such shares Shellder's typing, base stats, Pokédex data, icon, cry, shiny palette, and learnset. It evolves into Graag with a Water Stone.
While it appears to be the intended evolution for Esplime, because of its index number and unedited evolution data Esplime can never evolve into Declime, and Declime will evolve into Graag.
Declime's backsprite is completely blank, so it will be invisible if it's the first Pokemon sent out on the player's side, or if it is not the first it will use the backsprite of the last Pokemon sent out but with the wrong palette. It shares this trait with its (unintentional?) evolution, Graag.