Saslash is a Poison type Pokémon. Saslash is No. 088 on the Pokédex. It is a sprite-swap of Grimer, and as such shares Grimer's typing, base stats, Pokédex data, icon, cry, shiny palette, and learnset. It evolves into Esplime starting at level 38.
Despite appearing to be an evolution of Yethrall, its index number and lack of evolutionary data editing means that you cannot get a Yethrall to ever become a Saslash, and Saslash can only evolve into an Esplime.