Helmasaur

Helmasaurs are a recurring mask- or helmet-wearing species of squat animals. Usually, they resemble quadrupedal dinosaurs, hence their usual English name, but have also been depicted as beetles and birds. In many games, the armor can be removed, allowing them to be hit anywhere on the body.

The Legend of Zelda: A Link to the Past
In The Legend of Zelda: A Link to the Past, Helmasaurs first appear in the Palace of Darkness. They are small orange dinosaurs with a large green mask covering their heads. Unlike later games, the mask cannot be removed. When Link approaches, they scurry quickly after him, and will do so from a great distance. At the heart of the palace is their leader, the Helmasaur King.

In A Link to the Past + Four Swords, indigo-masked Helmasaurs are spit out by an alternate version of the Helmasaur King in the Palace of the Four Sword.

The Legend of Zelda: Link's Awakening
In The Legend of Zelda: Link's Awakening, Helmasaurs are known as Iron Masks, and first appear in Angler's Tunnel. They are small and spherical with two stubby legs and large, pointed masks. The masks can be removed with the Hookshot, which becomes a recurring element in the series. Once it is removed, it is shown that the Iron Masks are otherwise featureless, and they will helplessly walk around with a surprised look on their faces. In Link's Awakening DX, They are colored red. Additionally, a mini-boss in both Angler's Tunnel and Turtle Rock, called Cue Ball, is seemingly a combination of an Iron Mask and a Water Tektite.

The Legend of Zelda: Majora's Mask
In The Legend of Zelda: Majora's Mask, Helmasaurs are known by their Japanese name, Hiploop. They appear as large yellow and green beetles with three wing plates and red faces. They walk along narrow bridges, and charge at Link when they see him, but can be blocked with a shield. If they successfully damage him or run into a wall, they will rear up on their hind legs while making a snorting noise. They are initially found in Woodfall, where they lack masks and as such are defenseless, but in Stone Tower Temple they have blue masks, which can be removed with the Hookshot.

The Legend of Zelda: Oracle of Seasons
In The Legend of Zelda: Oracle of Seasons, Iron Masks appear in Unicorn's Cave. Here, their masks can be removed with the Magnetic Gloves.

The Legend of Zelda: Oracle of Ages
In The Legend of Zelda: Oracle of Ages, Iron Masks appear in Moonlit Grotto and Jabu Jabu's Belly. Their masks can be removed with the Switch Hook or Long Hook, but if they are hit anywhere other than the mask, Link will just switch places with the creature.

The Legend of Zelda: Four Swords
In The Legend of Zelda: Four Swords, Helmasaurs resemble an expansion on the design used in previous Game Boy line games. Their feet now resemble bird feet, and their now have parrot-like faces if their masks are removed with the Hookshot. Their bird-like design may be to tie in to how the Helmasaur King was redesigned as a bird called the Helmaroc King in The Wind Waker. They now charge around in large straight lines.

The Legend of Zelda: The Minish Cap
In The Legend of Zelda: The Minish Cap, Helmasaurs look and act the same as in Four Swords. They are first found in a cave at Mount Crenel's Base, and their masks can be removed with the Gust Jar.

The Legend of Zelda: Twilight Princess
In The Legend of Zelda: Twilight Princess, Helmasaurs are small green dinosaurs that wear hole-covered gray armor across their backs. It can be removed with the Clawshot, at which point Link can carry around the armor and throw it like a rock. They appear in northern Hyrule Field, the Lakebed Temple, and the City in the Sky. The last of these locations also features a larger version with irremovable armor, the Helmasaurus.

The Legend of Zelda: A Link Between Worlds
In The Legend of Zelda: A Link Between Worlds, Helmasaurs have the same design as in A Link to the Past, but are somewhat less aggressive as they do not chase from as far. Their masks can now be removed with the Hookshot, showing them to have blank white eyes. They again first appear in the Dark Palace, which is now led by another giant Helmasaur called the Gemesaur King.

The Legend of Zelda: Tri Force Heroes
In The Legend of Zelda: Tri Force Heroes, Helmasaurs are found in the Sky Realm, and resemble their appearance in A Link Between Worlds. However, they are much more aggressive than before, running after Links almost as fast as they can run away, and thus not giving a lot of time for the pursued Link to remove their masks. However, another Link can remove their masks with the Gripshot.