Tentacool, a Jellyfish Pokémon. 99% of its body is made up of water.
– Ash’s Pokedex
Tentacool has been in every regional Pokedex until Gen V (the Unova dex has no Pokemon outside of Gen V). It’s present on almost every water route, so when you surf, it’s likely you’ll meet lots and lots of Tentacool (to a point where they get annoying and I’d have to keep using repels). In HeartGold, I was able to grind my Venusaur up to a high level by killing lots of Tentacools (back before I cared about EV-training, haha).
Tentacool kinda reminds me of a helmet. When I first saw it, it took me a while to figure out that its eyes are down there, I thought the red things on its body were its eyes at first. Looking close at it, it looks kinda disgruntled.
Its family was the only Water/Poison type before Qwilfish came along. It can get Rain Dish ability in the Dreamworld, which makes it useful on a rain team I suppose.
Stat-wise, it’s got lots of Sp Defense (which makes Sp Def EV training easier, haha), decent speed, and not much else.