Black Flies (ブラックフライ Burakkufurai), also known as Flies for short, are one of the most common enemies, found in almost all chapters. They can naturally spawn in The Basement. They also come in sort of multiple variants.
Black Flies buzz around the room randomly, making buzzing noises, often moving away from the player. They cannot damage Isaac at all, even by touch, making them completely harmless. However, they can turn into relatively dangerous Pooters if they fly around the Poop for too long or come in contact with a golden poop.
- They, along with few variants such as Attack Flies, can be spawned by multiple enemies as well as bosses including The Duke of Flies, The Husk, Mulligans, Hives, Swarmers, Gurdy, and Pestilence.
- A pair of Black Flies has a chance to spawn at the beginning of the boss fight with Monstro, The Duke of Flies, and few other bosses.
- Black Flies has 3.11% chance to appear from the Slot Machine.
- 3 Black Flies has a chance to spawn in the Treasure Room. (?)
- They appear in the original game.
- Black Flies, along with other type of flies, are one of the enemies with lack of champion variants.
- Same apply to Spiders and few other monsters.
- From the original game, few Black Flies can be seen from the menu screen before starting the game.
- In Rebirth, however, never appear in the menu screen but few sprites still can be found in the game files.