I'm probably wrong, but... Krabby? I'm gonna make a couple anime references here:
I may not, at first, seem to fit in with my friends, When Ash first catches Krabby, it doesn't fit in his party because he already has 6 pokemon, so it goes to Oak's lab
However, it may be quite fitting. ?
Second of three, though the first true one, In gen 1, Ash catches 3 water types: Squirtle, Krabby, and Lapras, but Squirtle joined Ash willingly, so it wasn't a "true" capture
In the rain I'll have my fun. Water type
Watch out! Don't step on me! It's a crab...
I may be weak now not fully evolved
(Though I can still teach you a lesson) can still attack
But soon I will master the art of the battle. Kingler