The Flygare (canon model name) is a monster first encountered after exiting Gustaph Dahl park in Chapter 3, heading for Waspet Gardens. It is a form of twitcher strapped down to an upside-down bed hovering over the ground. The creature seems to have some form of control over where the bed travels.
It has two forms of attack. The first is attacking Simon with two scissors if he gets too close, while the second is launching some of form of acidic projectile. They make a tell-tale 'roaring' grunt, when Simon is in the area, and the splattering of their projectiles only makes it easier to know when one is around.
Evasion is a viable tactic against these creatures in open areas, particularly to conserve ammo. However, in tighter corridors, they become a menace with their accuracy. Focusing on one of these creatures, you can observe that they have a cooldown period between attacks. When a Flygare is about to spit its projectile, its head will begin to spasm; this is the player's cue to sidestep an oncoming shot.
Flygares are one of few enemies to actively evade and dodge Simon's attacks. After getting hit or if the player aims at them for long enough, they will quickly move about and change positions. In the open when there are at least two of them, they will also try to flank the player and fly in circles around them, attacking them all the while. The front of their bed as well acts as a "shield" against bullets, and it is necessary to fire in between the rails to actually hit them.
After the Flygare has launched an attack, it is wise to line up a few shots with the handgun, closing in if necessary. Keep in mind that if you close distance with a Flygare, it may be compelled to begin flying after you, trying to stab Simon with its scissors.
In addition to their first appearance, Flygare show up in Waspet Gardens after digging up the key to the high-rise apartments, (where they are better outran than fought, thanks to the openness of the park, and their number in one area), and later in both the Saxxon Avenue and Hanson Square subway stations. A few appear in Kirkville toward the end of the game, and a large number of them (about seven) also appear on Preston Road in Doctor Mode, as well as in front of the Apartments toward the end of Doctor Mode.
The Flygare is likely meant to symbolize Simon's growing insanity, as well as his crippled state. A common tactic used on insane patients in asylums is to restrain them to their beds, evidently a nod to Simon's mental state. The creature's inability to move without the assistance of the bed is likely a nod to Simon's wheelchair.