Tentacool is too weak to deal much damage. :S But it could probably survive longer than most Pokemon, so it might pay off. Too bad there aren't many other good Rock types available at that point. Graveler and Nosepass are your best options, but they're both tricky to obtain and you likely won't just randomly run into them unless you happen to break a lot of rocks.
I thought Chimecho was a shiny Pokemon, because of how long it took me to find the damn thing. (Didn't even know it was there.)I got so excited when I randomly found a Chimecho because I had no idea what it was and thought it was some rare, super powerful Pokemon. XD
*draws @Octy;'s magnificent ass*