Boom Flies are much larger than normal Flies. Rather than trying to follow you, they will instead fly around the room diagonally, bouncing off walls. They have considerable health, taking at least six 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 your distance from it and maintain considerable range; if you stay too close to it when you 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.
Red Boom Fly
Red Boom Flies move identically to regular Boom Flies, but will shoot 6 projectiles on death instead of exploding. The projectiles always have a set trajectory pattern so you can position yourself for safety.
- The Skatole item slows down Boom Flies and Red Boom Flies drastically, but they will still explode on death and can damage Isaac.
- If you kill a Red Boom Fly before it moves, it will explode like a normal Boom Fly.
- If you 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 you encounter after picking up Bob's Curse. Does not apply for Red Boom Flies.