I think that the spot of "my favorite Pokemon" has now been given to Shuckle. I'm sure all of you know about its colossal Defenses, allowing it to stand up to a crapload of attacks, but I just found out about the massive damage a Shuckle can do. You're probably wondering, "How the hell can a Pokemon with one of the crappiest Attack ratings in the entire game possibly cause any damage?" Well...
"Shuckle has the highest Defense and Special Defense stats of any Pokémon, with a max of 614 in them with beneficial natures (which are also the highest non-HP stats in existence)." This is already known. But, "After using Power Trick, Shuckle has the highest Attack of any Pokémon with a max of 614 in it with beneficial natures (To compare, Deoxys's Attack form's maximum Attack stat is 504)." And then, you can raise that even more if you Skill Swap Pure Power or Huge Power, which can give it a maximum Attack stat of 1228.
Under these circumstances (and assuming that the above has already been done), "a level 100 Shuckle can potentially deal the most damage in one single attack through the use of numerous stat boosters, by using Helping Hand, Metronome held item, and the Defense Curl/Rollout combo. On the 5th impact of Rollout, if used against a level 1 Ledyba or Yanma that have been hit with negative Defense modifiers (such as Screech), it can deal over 315,000,000 damage." If you're thinking it's useless seeing as no one uses a Ledyba/Yanma in their team, "The fifth hit of the Rollout combo would be enough to knock out 490196 Blisseys."
If you're wondering what some of the terms above are, Power Trick is a move that switches the user's Attack and Defense stats. Skill Swap is a move that switches the Abilities of two Pokemon. Huge Power and Pure Power are Abilities that doubles the user's Attack stat (although Huge Power's multiplier is reduced to 1.5x when Skill Swap is used, making Pure Power the better choice). Helping Hand is a move used only in Double Battles that increases the power of the partner's move by 1.5x. The Metronome is a held item that raises the power of a move by 10% if it is used repeatedly, capping at 20 repeated uses (not sure of the exact multiplier). Finally, the Defense Curl/Rollout combo is when Defense Curl is used, followed by Rollout the turn after, which doubles Rollout's power.
So yeah, Shuckle = Rape. Also, I'm well aware the scenario listed above is practically impossible. I just thought it'd be a nice little chunk of information.
Info gotten from Bulbapedia before you think I actually went and researched ALL of this on my own.