A Seaking is a much like a koi goldfish, only it has a horn at the top of its head. It evolves from the Pokemon Goldeen at level 33 and can also learn an HM move (Waterfall). This move allows the trainer to travel up and down waterfalls at will. It also learns the attack Horn Drill, which, if it hits the opponent of a lower level, results in a one-hit KO. It has since become a meme under unknown circumstances, accompanied with the words, often in capital letters, "FUCK YEAH!" Though this went to a little bit higher level when it was revealed in the Diamond and Pearl games you could add letters to the Pokemon's entrance into battle, allowing you to use up to eight letters. Seaking has since been mixed with other Pokemon, such as Slowpoke, Bidoof, and/or Mudkip.
Gamer 1: Dude, I was using the Super Rod in the Safari Zone... You'll never guess what I found.
Gamer 2: I dunno... Slowbro? Dratini?
Gamer 1: SEAKING!
Gamer 1&2: FUCK YEAH!