A battle plane type bird robot last seen in "SKY CHASE ZONE" from "Sonic 2". A whole bunch of them can be shot out of Metal Sonic's weapon unit, "Metal Carrier", in Episode II. — Profile, Sonic the Hedgehog 4: Episode II website
Balkiry Badnik's design is a hybrid of a bird and plane. The red and grey metallic body have wings on each side, a vertical stabilizer and two rotors on its back, which makes the Badnik move on medium or high speed. The head has small eyes facing front and a yellow bird beak. They have two support legs with small wheels that resemble eagles' feet.
Balkiry's appearance in Sonic the Hedgehog 4: Episode II is more detailed, as now the support feet are removed and it has received two extra wings in the vertical stabilizer. From Sonic Lost World though, Balkiry once again retains its cartoony design from previous games, only the wheels are not present on its feet.
Sonic the Hedgehog 2 (16-bit)
The first appearance of this Badnik was in the 16-bit version of Sonic the Hedgehog 2, where it served as an enemy. This time around, this Badnik is referred to as Balkiry (バルキーン,Barukīn?). In this game, the player encounters them in Sky Chase Zone, where the player controls Sonic with his Tornado that is piloted by Tails (and vice versa).
In gameplay, the Balkiry Badniks fly fast in the opposite direction of the playable character. At the beginning of the Zone, the Balkiry Badniks appear one at a time, but as the Zone progresses, they appear in larger groups of two or three, and at much faster speeds. However, the Balkiry Badniks have been given a simple pattern; they simply charge towards their target like a missile, from one side of the screen. As such, they are not particularly dangerous, although some of them tend to move quickly and can take the player by surprise. Also, upon their destruction, they release an Animal.
In Sonic the Hedgehog 4: Episode II, the Balkiry Badniks are featured in the first act and boss fight of Sky Fortress Zone. In this game, the Balkiry's design and its behavior is slightly different from Sonic the Hedgehog 2; they are now launched from the Metal Carrier and cascade down on the player from the top of the screen. However in the Boss Act, some Balkiry Badniks behave just as they did in Sonic the Hedgehog 2.
In the Wii U/PC version of the game, the Balkiry Badniks appear as obstacles flying by in the skydiving sections of Desert Ruins Zone 2. In Tropical Coast Zone ? and Sky Road Zone 3 however, they charge from the right in string formations towards Sonic when he is maneuvered through the air, though the player can destroy them from above by performing Spin Attack. Balkiry Badniks also appear in Hidden World Zone 2, where the player can only avoid them while piloting the Tornado.
In the Nintendo 3DS version of the game, Balkiry Badniks appear in Sky Road Zone 1 and 3. In Zone 1, they will charge forward until they come across the ceiling, wall or corner where they will turn around and head in the other direction. Here, the player has to destroy them to unlock a switch in a case. In Sky Road Zone 3 though, Balkiries will fly towards Sonic in different string formations, which the player can only avoid while controlling Sonic on the rocket.
In Sonic Runners, Balkiry Badniks are one of the most common Badniks in the flying type character's stages. Like in previous games, they charge from the right direction, and appear separately or in groups.
The Balkiry in Sonic Runners come in three types. Aside from the regular types, there is golden Balkiry Badniks that give 300 extra points each when destroyed, and black ones called Super Balkiry that only Color Powers and power type characters can destroy. Any type of Balkiry contains Animals inside them.
In the Sonic the Comic series published by Fleetway Editions, the Balkeries are a part of Dr. Robotnik's Badnik army, here serving as the standard flying units among the doctor's military forces. Unlike most other Badniks in the series, the Balkeries' design remain fairly consistent during the comic's run.
In Sonic X, a robot called E-11 Beacon is based on Balkiry though it has a purple-colored scheme.
In Sonic the Hedgehog 2, Balkiry has unused in-game sprite showing its landing pose, that can be found in the game's coding. It is possible that they were originally intended to start flying from this pose at Wing Fortress Zone, but the movement has then become unused for unknown reasons.
The unused sprite is also used when you are placing a Balkiry in Debug Mode.