|Guppy||Beelzebub||Super Bum||Yes Mother?||Bob||Fun Guy||Leviathan||Conjoined|
|Spun||Seraphim||Oh Crap||Bookworm||Spider Baby||Adult||Stompy|
Isaac turns into a giant humanoid fly and gains flight. While in this form, most types of enemy flies will automatically be converted into Blue Flies. Enemies such as Boom Fly and its variants will become friendly and be brought with Isaac to other rooms and floors.
Requires any combination of three of the following items to be collected:
|Jar of Flies||5.100.434||Bug catcher||Killing an enemy adds a fly to the jar, up to a maximum of 20. On use, releases Blue Flies equal to the number of flies in the jar.||2|
|Plum Flute||5.100.650||Play time!||Summons the boss Baby Plum to fight for Isaac in the current room.||2|
|???'s Only Friend||5.100.320||Controlled friend||Spawns a controllable familiar that deals 37.5 damage per second on touch. It can be moved using the shooting directional keys||2|
|BBF||5.100.272||Big Beautiful Fly||Spawns a familiar that flies around the room in a zig-zag pattern and explodes on contact with an enemy. Respawns after ten seconds.||1|
|Best Bud||5.100.274||Sworn protector||When hit, spawns a quickly orbiting attack fly similar to Forever Alone for the current room dealing 75 150 damage per second.||0|
|Big Fan||5.100.279||Fat protector||Spawns a large orbital familiar that blocks enemy shots and deals 30 damage per second to enemies.||2|
|Distant Admiration||5.100.57||Attack fly||Spawns an attack fly that circles further out than Halo of Flies, but closer than Forever Alone, dealing 75 damage per second.||2|
|Forever Alone||5.100.128||Attack fly||Spawns an attack fly that orbits a long distance from Isaac, dealing 30 damage per second.||1|
|Halo of Flies||5.100.10||Projectile protection||Spawns two Pretty Flies that block enemy shots and deal contact damage to flies.||3|
|Hive Mind||5.100.248||Giant spiders and flies||Increases the size of Blue Spiders and Blue Flies and doubles the amount of damage they deal. Also increases the effectiveness of fly and spider familiars.||2|
|Skatole||5.100.9||Fly love||Flies become harmless or less dangerous depending on the type.||0|
|Smart Fly||5.100.264||Revenge fly||Spawns an orbital familiar that blocks enemy shots. Upon taking damage, the familiar will pursue enemies for the rest of the room, dealing 22.5 damage per second.||3|
|The Mulligan||5.100.151||They grow inside||Tears have a 1/6 chance of spawning allied Blue Flies when they hit an enemy.||3|
|Friend Zone||5.100.364||Friendly fly||Spawns a white attack fly that orbits somewhere between Distant Admiration and Forever Alone, dealing 45 damage per second.||1|
|Lost Fly||5.100.365||Lost protector||Spawns fly familiar that moves in a straight line and circles around the first wall or obstacle it hits, dealing 105 damage per second on contact.||0|
|Obsessed Fan||5.100.426||Follows my every move...||Spawns a familiar that follows Isaac's movements on a 3 second delay and deals contact damage to enemies.||0|
|Papa Fly||5.100.430||Turret follower||Spawns a familiar that follows Isaac's movements on a 3 second delay, firing tears at nearby enemies.||1|
|Angry Fly||5.100.511||He's violent||Spawns a fly familiar that orbits around a random enemy and deals 30 damage per second to enemies it comes in contact with.||1|
|Bot Fly||5.100.629||Defense drone||Spawns an orbiting fly familiar that fires shielded tears at incoming enemy projectiles.||3|
|Fruity Plum||5.100.649||Bouncy friend||Gives Isaac a miniature Baby Plum familiar that propels itself diagonally around the room, firing tears behind itself as it travels.||1|
|Psy Fly||5.100.581||Flamboyant protector||Spawns a fly orbital familiar that chases and deflects enemy shots and converts them into homing tears.||3|
|The Swarm||5.100.693||Infest||Spawns eight orbital flies, which turn into Blue Flies after they block a shot. Each time a room is cleared, spawns another orbital fly.||2|
|Parasitoid||5.100.461||Egg tears!||Adds a chance to fire an egg sack which creates slowing creep and spawns a Blue Fly or Blue Spider upon hitting an enemy.||3|
|YO LISTEN!||5.100.492||Yo listen!||+1 luck. Spawns a fairy familiar that points out Secret Rooms, Crawl Space entrances, and tinted rocks.||2|
- The player starts with this transformation in the Solar System challenge.
- The Pretty Fly Pill(or gaining a pretty fly through a slot machine) does not count toward this transformation.
- Beelzebub is the name of a Demonic fly who is known as "Lord of the flies" and is known as one of the 7 princes of hell. Beelzebub is also another name for the devil.
- In modern Catholic tradition, Beelzebub is regarded as one of the 7 princes of Hell; however, the origins of the name Beelzebub actually dates back to an early Jewish insult for worshippers of a Canaanite Deity Ba'al 'Lord', or Ba'al-Zvul 'Lord of the manor/dwelling', calling him Ba'al-Zvuv, 'Lord of the flies'.
- The achievement 'Lord of the Flies' is a reference to this.
PC W2DW TA79 (Allows Isaac to become Beelzebub in The Caves XL. First two Treasure Rooms are Big Fan and Attack Fly, one of the Treasure Rooms in Caves XL is Halo of Flies)
PC 9CM4 JDBL (Last fly item collected on Flooded Caves I)
PC B14A Q44Y (Also contains four Guppy items)
PCEVLC BNBE (First three Treasure Rooms start with Psy Fly, Lost Fly, and Halo Of Flies)
Switch TF11 R19Z (First three floors Treasure Rooms contain Smart Fly, Forever Alone, and Infestation)
|The Binding of Isaac: Rebirth|
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|