Archie is ez if you have grass types or electric types.
Almost everywhere in the grass, especially the long grass.
use dive go in the deep sea grass he will be in the grass
In the grass on jagged path.
Electric and Grass type attacks are effective against Water types. Water type attacks are bad against Grass, Dragon and other Water types. Note that almost all Water Types can learn an Ice type move, so be careful when sending in Grass types to counter them.
Bug types Pokemon can use normal and Grass type primarily, a few can use Flying or a select other type depending on the Pokemon.
about 500 types of grass.
All of them, in nature.
you will get it in sapphire. it can appear in wild grass if you are lucky.
Treecko, Tropius, Seedot, Oddish.
By capturing all of the water types of it.
electric and grass are all I can think of