Number 1) Wooper. reason: other than cuteness, I like wooper because of nostalgia. gen 2 was and still is my favorite, and wooper was one of my first Johto Pokémon.

Number 2) Togedemaru. reason: because of the cuteness!

Number 3) Bidoof. reason: well, it's so cute! how could someone not like Bidoof? *because they're everywhere...*

Number 4) Rowlet. reason: grama type? check. Owl? check. sphere? check. starter? yesssss…

Number 5) Chespin. reason: why else? if anyone remembers the XY anime, I'll just let you take a guess.

Number 6) Mew. reason: Pokémon: the first movie. what an adorable Pokémon.

Number 7) Dedenne. reason: see number 5.

Number 8) Umbreon. reason: Shadow... fox? TELL ME HOW TO GET ONE IN REAL LIFE!!!

Number 9) Mudkip. reason: *cough* Axolotl. *cough*

Number 10) Espurr. reason: see numbers 5 and 7... but really, why do so many people think this is creepy?

Number 11) Quagsire. reason: evolves from wooper... yeah. well, guess what I had for 75% of Johto!

and finally...
Number 12) Mareep. reason: ovelha, ovelhas Pokémon? I think yesss...