Diglett
Dugtrio
Since Route 11 is blocked you'll have to take Diglett's Cave to reach Viridan Forest. There is another Aide in these Caves and he will give you the HM 05 which can teach a Pokemon the Flash ability. What it does is it lights up dark places such as Rock Tunnel which is later on in the game.
Items found in Viridan Forest:
HP UP
Moon Stone
