(All information from Bulbapedia)

Treecko

  • Treecko has the lowest base defense of all unevolved starter Pokèmon.
  • Treecko and its evolutions are the only Grass-type Pokèmon that belong in the Dragon Egg Group.

Torchic

  • A pre-alpha sketch from before Pokèmon Ruby & Sapphire that was released portrays a different Torchic with large floppy ears and a flame shaped marking on the back of its head.
  • Torchic is the only unevolved starter Pokèmon available in the wild, being found on the Pokèwalker course sightseeing along with Pikachu. (Prior to Pokèmon Platinum, it was also the only starter allowed in Amity Square, along with Pikachu.
  • Torchic is the first starter Pokèmon and only Fire-type starter Pokèmon to be based on a bird.
  • Torchic is the only first stage of a starter Pokèmon that has a gender difference (though its own is very easily missed, being only a one pixel difference)
  • It also is in the only starter Pokèmon evolutionary line in which all members have gender differences.
  • Torchic is the lightest Fire-type Pokèmon and the lightest of the basic forms of all starter Pokèmon.

Mudkip

  •  Mudkip has the highest attack out of all starters at its base form.
  • In a poll conducted by Nintendo of Europe, Mudkip was voted as the fan favourite starter.
  • Mudkip is the subject of a popular internet meme known as "So I herd u liek Mudkipz?"