Meltdown
Meltdown is a Modern Harbinger added in The Reheated Update that appears as a boss in the 
Burning Basement.
Behavior
Phase 1
In his first phase, Meltdown floats around the room, performing various attacks:
- Quickly fires a spread of 3 projectiles in a cone shape towards Isaac.
- Lobs an indestructible barrel a short distance towards Isaac, which leaves a trail of gunpowder. He will then cough a green burning coal to ignite the trail and light the barrel, which explodes in a ring of 8 fires.
- If there are any sources of fire, the gunpowder can be ignited and the barrel blown up early. Meltdown will still lob the coal as usual.
- Charges horizontally to one side. After disappearing from the room, he will send out a decoy horse from the opposite side, which flies in lined up horizontally to Isaac and explodes in a plus pattern once it hits a wall, any enemy, or Isaac. The decoy will also explode prematurely if it takes 10 damage.
As Meltdown takes damage, he will spawn Falafels in-between attacks, flinching as he does so. For every 10 HP lost, he will spawn an extra Falafel. He will spawn as many as possible at once for the total culminated amount of damage taken during an attack after the attack ends. Meltdown will not perform the same attack twice in a row.
Phase 2
When Meltdown's health goes below 132 HP, he will rip out the hobby horse stuck in his body and toss it on the ground in anger. This triggers the bomb in the horse's maw, which explodes in a harmless flash of light, charring the whole room. After this, he will continue the rest of his fight as a floating skeleton, referred to as his "Raptured" form.
- Meltdown gains strong damage reduction during the length of the entire sequence.
Meltdown now floats erratically around the room, constantly emitting rotating rings of 5 green flames around him.
- Projectiles will periodically travel down from the top of the room in 4 slanted lines (two at the middle, two on the sides). These projectiles leave a visual trail on the ground, marking their trajectory.
- Shortly after the transition, a nuclear bomb will drop harmlessly at a random position in the room. It deals no contact damage.
- Meltdown will move to pick it up, flying around the room while holding it. After a moment, he will stop to throw it a short distance towards Isaac.
- The bomb will explode as it lands, releasing fast-moving streams of green fire in the cardinal directions and slower streams in the ordinal directions.
- Another one will drop down again in another location shortly after the explosion if Meltdown is still alive.
- If the bomb is on the ground when Meltdown dies, it explodes on the spot releasing fire as usual.
Notes
- While in his phase 2 transition, Meltdown can still be killed despite the damage reduction if Isaac has high enough DPS, skipping the second phase.
- Meltdown takes reduced damage from his explosions.
Spawns
Falafel
Falafels are a special variant of 
Morsel spawned by Meltdown, which behave identically to Morsels despite their unique appearance. They are spawned by Meltdown as he takes damage between attacks, and will chase after Isaac.
Unlockable Achievements
Video Showcase
Trivia
- According to the developers, Meltdown represents a nuclear apocalypse, similar to classic old war/conquest but more dangerous and insidious. He represents the nuclear winter, brought on by rising tensions from the previous three horsemen.
- The nuclear bomb that spawns during Meltdown's second phase is referred to as "Davy Crockett" in both the game files, as a reference to the Davy Crockett weapon system (a tactical recoilless gun meant to fire tiny nuclear warheads).
- Meltdown's eyes and tongue, his horse's eyes and decoy horse's eyes all glow in the dark when the room or floor is under Curse of Darkness. In his second phase, his whole head also glows with light in the dark.
- Meltdown may be inspired by the character Melting from the game Nuclear Throne, as it bears a resemblance to them and appears to be radioactive.
- Meltdown is voiced by RENREN, the composer and sound designer for Fiend Folio.
- After Meltdown switches to his 2nd phase, a tiny face-shaped scorch mark appears on the floor behind Meltdown. This scorch mark is identical to the one created after killing
Hush.
Gallery
Meltdown's appearance while charging.
The decoy horse sent out after Meltdown charges out of the room.
Meltdown after unsticking himself from his hobby horse.
Meltdown's "Raptured" form.
The bomb that spawns during Meltdown's second phase.
Drawing of Meltdown in the Bestiary and on Isaac's last will.
Drawing of "Raptured" Meltdown in the Bestiary and on Isaac's last will.
Meltdown's health bar icon if Enhanced Boss Bars is installed.
"Raptured" Meltdown's Enhanced Boss Bars icon.
 Bosses 
| |
|---|---|
| Chapter 1 | Buck - Honeydrop - The Whispers - Griddle Horn - Buster - Meltdown |
| Chapter 1.5 | Ghostbuster - Cacamancer |
| Chapter 2 | Battie - Kingpin - Slinger - Monsoon - Aquagob |
| Chapter 3 | The Organization - Gutso the Great - Luncheon - Pollution - Tsar - Junkstrap |
| Chapter 3.5 | Warp Zone - Dusk - Madomme |
| Chapter 4 | Basco - The Sun - Peeping - Cacophobia |
| Chapter 4.5 | Mr. Dead |
| Minibosses | Psion - Gravedigger - Hermit |
| Vanilla Boss Champions | Golden Plum - Ghost Larry Jr. - Mucus Monstro - Technopin - Albino Widow - Beehive Fistula - Possessed Hollow - Wine Husk - Kidney of Infamy - Alien Loki - Fiend Mom - Alien Lokii - Grinch Krampus |