This is the second last evolution of Eevee and the last one of the Sinnoh Pokedex. Glaceon is an Ice Pokemon and the only way to get this evolution is very similar to Leafeon. You have to find an icy rock in Sinnoh( I think it's near Snowpoint or on the route before getting to Lake Verity). Then it's the same thing: level up Eevee around the icy rock.

Enjoy the art!