Boom Flies are much larger than normal Flies. Rather than trying to follow Isaac, they will instead fly around the room diagonally, bouncing off walls. They still deal contact damage. They have considerable health, taking at least 6 initial tears to go down. They explode upon death, typically killing all other monsters and dealing a full heart of damage in a small radius.
When fighting a Boom Fly, it is advised to keep Isaac's distance from it and maintain considerable range; if he stay too close to it when he kill it, it will explode and deal damage to Isaac. Due to this, fighting a Boom Fly when the player has very low range is quite risky.
Eternal Champion Behaviour
Eternal Boom Flies cause a gigantic explosion upon death, significantly larger than a Mr. Mega bomb.
- The Skatole item slows down Boom Flies and Red Boom Flies drastically, but they will still explode on death and can damage Isaac.
- They can be spawned by the blue champion variant of Fistula.
- Boom Flies' eyes are larger from the original game. In Rebirth, however, their eyes are smaller.
- If Isaac collected Bob's Curse and kill a Boom Fly after (at any given time), the Boom Fly's explosion will be green, and its the same for all the Boom Flies he encounter after picking up Bob's Curse. Does not apply for Red Boom Flies.