Octorok

The Octorok is perhaps as much part of the Legend of Zelda as Link or Zelda, having appeared in every Zelda game except Twilight Princess. It's an octopus-like creature that shoots rocks from its snout. In the 2D Zelda games, they seem to have adapted to living on land, and can generally be killed with one or two hits from the sword. That makes them as "normal enemies".

The Legend of Zelda: Ocarina of Time
Octoroks made their 3d debut in Ocarina of Time along with many other classic enemies. Although they still spit rocks, they live in the water. They had a much different form and were purple rather than red. They could be killed in a number of ways, the most common being using your shield to reflect the rocks they spit at you back at them. However, they can be killed with any projectile as well.

The Legend of Zelda: Majora's Mask
In Majora's Mask, octoroks return just as they did in Ocarina of time. But in Termina, shooting an ice arrow at them will make them into a platform.

The Legend of Zelda: The Wind Waker
In The Legend of Zelda: The Wind Waker, Octoroks take an all new squid-like form that shoot rocks at you, as always. When out in the ocean, there are Big Octos, these creatures shoot bombs at you instead of their normal rocks. However, if you are going at a good speed, their attacks pose little to no threat.

The Legend of Zelda: Four Swords Adventures
In Four Swords Adventures, the Octorok came in three versions. The red one, which was the original. There was also the purple one which stood still for a few seconds until launching four stones at a row, right towards Link. The blue one was even more tricky. It shot at all four directions at the same time, and required 16 hits before acually getting killed.

The Legend of Zelda: The Minish Cap
In The Minish Cap they appear in three forms: Blue, Red, and Gold. The blue ones are tougher then the red ones, but the gold are the toughest and can only be found by fusing kinstones.

Quote from The Legend of Zelda: The Minish Cap Octorok figurine: "Appears in various areas. There are red and blue ones. They've appeared in every Zelda game to date. They spit rocks, so be careful."

The Legend of Zelda: Twilight Princess
Twilight Princess is the very first game in the series in wich Octoroks are totally absent; the monsters that were thought to be octoroks in other locations are an entirely different species known as toadpolis. Although toadpolis act similarly to octoroks, they resemble developing tadpoles and they actually swin underneath the surface of the water. They are only found in a few place and there are smaller ones and larger ones.

The Legend of Zelda: Phantom Hourglass
In Phantom Hourglass, Octoroks go back to their original form, despite the game being a direct sequel to WW(in which they were very different). The game actually presents them in a 3d version of this form for the very first time. In the game, they come only in their Red versions, but are more of a hazard than ever because of their rapid rock spitting.