Plan C 
Effects
- Upon use, deals 9,999,999 damage to every enemy in the room, then kills Isaac 3 seconds later.
Notes
- Plan C does not kill both phases of bosses like (The Lamb) The Lamb, (Hush) Hush, (Ultra Greed) Ultra Greed, and (Mega Satan) Mega Satan, and is most useful when used during the last phase of these multi-phase bosses.
- For the game's sake, a run is not truly over until Isaac's Last Will appears. This means that some bosses that might seem to finish their death animations after Isaac dies, such as (Removed in Repentance)Ultra Greed, will still be technically killed and will still give their completion marks, even if Isaac does not enter the Final Boss Chest.
- Some bosses have special interactions with this item:
- Attempting to use this item to kill (Delirium) Delirium will not work. Its death animation is much longer than the time between using Plan C and Isaac's Last Will appearing, meaning Isaac will die first and it will not count as a kill. Having extra lives that revive Isaac outside the room will not help, either; Delirium must be fought again.
- However, items that revive Isaac in the same room he died in, namely
Lazarus' Rags (or being (Lazarus) Lazarus), (Added in Repentance)
Inner Child, (Added in Repentance)(Soul of Lazarus) Soul of Lazarus, and (Tainted Lost) Tainted Lost's (Added in Repentance)
Birthright, will allow Isaac to bypass this and kill Delirium with this item. In the case of Lazarus' Rags, though, the completion mark will go toward Lazarus and not the character originally selected.
- It is possible to kill Delirium by carefully timing pauses after each screen static. Each screen static plays a cutscene that continues to play even while paused, so by pausing and unpausing at the right timings, Delirium's death animation can be shortened to just under 3 seconds allowing for his completion mark to be awarded.
- (Added in Repentance) Will not work if used against (Ultra Greedier) Ultra Greedier as (Tainted Forgotten) Tainted Forgotten, (The Lost) The Lost, (Tainted Lost) Tainted Lost, or (Tainted Jacob) Tainted Jacob in his lost form.
- (Added in Repentance) Killing (Added in Repentance) (Mother) Mother's second phase with Plan C will kill Isaac just at the end of her death animation. Without an extra life no completion mark is awarded, but any extra life, including ones that spawn Isaac outside the room, will grant just enough extra time to receive the completion mark.
- (Added in Repentance) Killing (Added in Repentance)
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Dogma's second phase with Plan C will kill Isaac while the screen is faded to black. Any extra life item, including those that revive him outside the room, will work and still take him to (Added in Repentance) (The Beast) The Beast fight.
- (Added in Repentance) If used in (Added in Repentance) (The Beast) The Beast battle, Plan C will only kill the harbinger that Isaac is fighting on screen. It won't have any effect on the other harbingers nor The Beast itself (The Beast can still be killed if Isaac is fighting it when Plan C is used, and there is enough time to earn the completion mark).
- Invulnerable enemies and closed (Host) Hosts will not be killed by Plan C.
- Isaac's last will shows his last damage source as the cause of death, not Plan C. If Isaac has not taken damage or lost health from any source, Isaac's face is shown.
- Invincibility or the
Holy Mantle shield will not save Isaac from being killed.
- Some items that activate when Isaac reaches zero hearts, such as (Added in Repentance)
Heartbreak and (Added in Repentance)
Spirit Shackles, will not activate and save Isaac.
- Even if Isaac enters a trapdoor immediately after using Plan C, he will still die after arriving at the next floor.
- Plan C has an 80% decreased item pool weight, making it less likely to appear than other collectibles.
- Plan C is found in 8 item pools, the highest count amongst all items. Its lowered weight, however, offsets its presence.
Synergies
- (Added in Repentance)
Book of Virtues: Spawns 8 red wisps that shoot red tears at 12 damage per tear. Using Plan C will kill Isaac as expected, but wisps won't disappear if used with an item that grants an extra life.