Servine as a Snivy is Dewott as an Oshawott ex-best friend. He is 16 years old (17 in season 5 and later) and he is very strong and fast. He was later replaced with a female Servine, but he is a reference to a dead Servine who only appeared in Season 0.
He evolved with Dewott and Pignite at the beginning of Season 3.
He devolved with Dewott and Pignite when the series got cancelled, so Snivy was temporarily a Servine with Oshawott and Tepig.
Servine
As a Snivy