Boom Flies
Boom Flies are generally characterized by flying diagonally around the room bouncing off walls and releasing an attack upon death.
This page is about Boom Flies added by Fiend Folio. More information about Boom Flies in general can be found in the vanilla page.
Butt Fly
Butt Flies behave like regular Boom Flies, but will fart if lined up diagonally with Isaac, propelling themselves towards Isaac in a small charge and knocking him back. They will not propel themselves in the opposite direction of their current path if Isaac is behind them.
Butt Flies will also fart on death, dealing knockback.
Mightfly
Mightflies are upgraded 
Mayflies that behave like Boom Flies. On death, Mightflies pop into 3 spreads of 2 projectiles in a V pattern as well as a shower of projectiles. One of the pairs of projectiles will be aimed in Isaac's closest cardinal direction with the other 2 pairs evenly spaced from it.
Fossilized Boom Fly
Fossilized Boom Flies are rocky Boom Flies that drop to the ground upon death in the form of a stationary boulder while also setting its health back to full. This boulder deals no contact damage, but explodes into a small cluster of 6 rock projectiles after being destroyed. The boulders spawned by Fossilized Boom Flies do not need to be killed to clear a room.
Fossilized Boom Flies will also create rock bridges if destroyed over a one-tile wide pit.
Warhead
Warheads are yellow Boom Flies in the shape of a lemon that fly noticeably slower than their counterparts, and burst into a ring of 8 yellow projectiles and a large puddle of yellow damaging creep upon death.
Bunch
Bunches are a group of grape-like flies stuck together. They fly around the room in angled diagonal paths making uneven bounces off walls. On death, they burst into a ring alternating between 3 Grapes and 3 purple projectiles.
Grape
Grapes are tiny purple colored variants of Boom Flies that are less resistant to knockback and create a small explosion on death.
Doom Fly
Doom Flies are skeletal Boom Flies that release a ring of 6 boomeranging rib projectiles upon death.
Warble
Warbles are Boom Flies based on 
Scolex, and can only be damaged from its tail as it files diagonally around the room. On death, a Warble releases a cluster of short-ranged projectiles in random directions that hover for a moment before dropping.
Trickle
Trickles behave similarly to Boom Flies, but after taking 10 damage, it will fall to the ground while creating a large fart that deals knockback, and transform into its spider form.
While in its spider form, Trickles behave similarly to 
Level 2 Spiders, but will always chase after Isaac with quick erratic dashes. It will occasionally hop to release a ring of 8 blood projectiles.
Upon death in either form, it will release a ring of 12 blood projectiles. Trickles are most commonly encountered in their fly form, but can also be occasionally encountered starting in their spider form as well.
Droolie
Droolies are emetic variants of 
Sick Boom Flies. When close to Isaac, they will cough up 4 green projectiles towards him that create small pools of green creep on landing.
On death, it shoots out a ring of 6 green projectiles that also create small pools of green creep on landing.
Trivia
- Mightflies were originally from the unreleased Flooded Caves Overhaul MOD.
- Warheads and
Sourpatches are named after each respective brand of sour candy. - Grapes can appear with one of three possible expressions: angry, woozy, or happy.
- A Bunch will always spawn one of each upon death.
- Doom Flies were redesigned in the Reheated update to prevent confusion with the similar-looking
Bone Flies which were introduced in Repentance. - Warble was originally a part of the cancelled Morbus floor MOD, and was ported as a part of the Reheated update.
- Droolie is based on a very similar looking fly enemy from multiple Team Bugulon games.
- Mightflies have a unique appearance when encountered on the Boiler floor if the Fall from Grace MOD is installed.
Gallery
Butt Fly's appearance in Dross.
Mightfly's appearance in Dross.
The boulder spawned when a Fossilized Boom Fly is killed.
A Grape with a woozy expression.
A Grape with a happy expression.
Back view of a Warble.
A Trickle in its spider form.
Mightfly's appearance in Boiler.
Old version of Mightfly.
First iteration of Doom Fly.
Second iteration of Doom Fly.
Third and AB+ iteration of Doom Fly.
The original concept art for Warble, drawn by Xalum.
