Double posting isn't going to really help, I'm guessing, Scyther.
As for me, I decided to go with Water instead of Rock. Since this is my first time doing a monotype challenge, I thought that I should save a more difficult type for a later attempt.
I began as all trainers do in Pallet Town, where I was quickly summoned by Professor Oak to begin my Pokemon journey! Even before I saw the three choices before me, I knew that only one Pokemon type would suit me, and sure enough Squirtle, who I named Tsunami, became my new friend and partner!
I ran an errand for the professor in Viridian City and quickly headed for Pewter City. There I challenged and quickly defeated Brock, not only receiving the Boulder Badge and the Bide TM but also watching as Tsunami became a Wartortle! We left immediately for Mount Moon, caught a Clefairy to later use for Flash, and arrived in Cerulean City.
This place really seemed like my kind of town, as the gym was full of water Pokemon I would have traded all the money in the world to have! Wartortle, already in his mid-twenties, had little trouble dispatching Misty and her subordinates, and we continued our quest to Vermillion City.
I was a bit worried about the gym and its electric types, but had little problem with it - there was no way to enter the gym! Instead, I used Bill's ticket to come aboard the SS Anne and fight the bored passengers. Along with me was a new ally, a Magikarp caught with the aid of the Fishing Guru. He was weak, but with Wartortle's and my help, we would make him strong. Closing in on the Captain's quarters to see if he could help train me in the ways of cutting, I could sense that my rival and former best friend Gary was nearby...
My Team
;008; Tsunami Lv. 33
Water Gun
Bite
Withdraw
Bubble
;130; Gyarados Lv. 20
Bite
Tackle
Splash
EDIT: What's the deal, the monotype challenge not very popular? In any case, I'm made significant progress, so here I go!
When I came up to Gary on the SS Anne, I was a bit worried about the fight in store for me. Instead, my as-of-yet unnamed Gyarados sweeps through is team with devastating results! I leave Gary to mull over his pathetic loss and enter the captain's quarters. It seems that the poor guy's seasick, and I help him out with a nice backrub, and it seems to do the trick! The captain is very grateful for my help and rewards me with a Hidden Machine, Cut! I wave to all as the ship leaves port and look to my continuing adventure.
I notice that while my training has gone well, I have gone lax in my duty to Professor Oak and his incomplete Pokedex. I quickly snatch up a Spearow and trade it for the extremely rare Farfetch'd, but unfortunately for him, Dux serves no more purpose than becoming an HM Slave. With him I am now able to enter the Vermillion Gym and challenge Lt. Surge.
The trainers are far simpler to defeat than I imagined, but the sheer power of Surge's Raichu leaves me reeling on the first two attempts. The lieutenant slips up on the third rematch by not using Thunderbolt to his full advantage, and I quickly crush the electric mouse in the jaws of Gyarados! Another badge, another TM and lots more prize money, while Surge gracefully accepts the amusing loss. Who knew that even the power of thunder could fail against water?
With the town's usefulness to me exhausted, I return with my team to Cerulean, obtain a Bicycle courtesy of the Pokemon Fan Club President, and go to Rock Tunnel. No trainer that stands in my way gives me the least bit of trouble, and neither do the Pokemon that call the cave their home. I manage to encounter a low-level Onix, but run out of Poke Balls and have no choice to make it faint to keep my Gyarados growing.
Ah! Fresh air once again! Things get noticeably more depressing in Lavender Town, but seeing the Name Rater raises my spirits: Gyarados gets a name, Typhoon. I ignore the Tower for now and go straight to Celadon City. The first order of business is to visit the enormous Department Store. I pick up all the trainer essentials, a Poke Doll for later, plenty of Lemonade, every TM I can get, and a Water Stone. The TMs go in my PC with the others and I get myself an Eevee. I waste no time in evolving it into a beautiful Vaporeon and teaching it Ice Beam. My own aqua-teen trio and I find out that Team Rocket is up to no good, and I personally take care of Giovanni and his cronies.
Erika is next on my list, and not a single trainer can stand up to the high-level power of my team. She hands over the badge and Mega Drain and I leave a happy young man. With the Silph Scope ready, I make my way to the top of Pokemon Tower, banishing the spirits haunting the Channelers as well as making peace with Marowak. The Rockets make a hasty retreat and with Mr. Fuji free, so do I - but only after capturing a cute little Cubone.
I use the Poke Flute to defeat the Celadon-side Snorlax, drive him back to the mountains with slight disappointment (no Ultra Balls) and use the speedy Cycling Road to get to Fuschia with ease. I enjoy a brief walk in the Safari Zone but my goal this time is the Secret House, not the rare Pokemon awaiting me there. Surf goes right onto my renamed Vaporeon, Atlantis, and the Good Rod becomes ours. Rather than hunt for new water-types or track down the other Snorlax and Super Rod, I crush Koga in combat and prepare to head for Cinnibar, where my Dome Fossil seems to be pulling me. Meanwhile, Team Rocket has invaded Saffron City, and I may just be the city's last hope...
My Team
;009; Tsunami Lv. 37
Submission
Water Gun
Withdraw
Bubble
;130; Typhoon Lv. 37
Take Down
Leer
Dragon Rage
Bite
;134; Atlantis Lv. 37
Surf
Ice Beam
Double Team
Reflect