Is there anything special in the Rock Tunnel. One NPC talks about Shiny Voltorbs but I went though it skipping one of the girls and I never saw any shiny Voltorbs, should I go back in and look for them?
yes, you can get a shiny voltorb from there. it's a side quest, you're gonna have to beat that onyx that toss you out for not having flash.
take these steps:
1) beat every trainer and every wild pokemon encounter at least once.
2) go to the top middle area where there's usually a pile of rubble blocking a path.
3) beat the onyx (battle can be tough and annoying because you have to beat all the trainers and pokemon again if you lose).
4)the old man is rescued and he'll say he'll give you a shiny voltorb if you show him a lv 42 electrode and lv 42 pikachu plus CATCH 10 wild pikachu without logging off/exiting game.
5) go back to him with the 2 lv 42 pokemon in party and you'll get your reward.