Mercurius is a passive item added in The Binding of Isaac: Repentance.
Effects
- +0.4 speed up.
- Opens most doors after entering a room, even in rooms with enemies, allowing Isaac to leave at any time.
Notes
- While
Door Stop has a similar effect, Mercurius has the added benefit of opening the doors that Isaac did not enter through. - Does not open the Boss Rush door.
- Does not open any special rooms, including those that require pickups to unlock. Doors won't be opened even if they were open already (such as Treasure Rooms and Shops on the first floor, Sacrifice Rooms, etc.) or have been entered before.
- Does not open doors to Red Key or Cracked Key rooms if that door was created while there are enemies inside.
Synergies
- 4.5 Volt/Jumper Cables: Provides infinite charges by clearing some enemies then leaving the room, and repeating.
- Charm of the Vampire/Gimpy: Allows the possibility to farm health.
- Head of the Keeper: With enough patience, coins can be farmed.
- Tainted Keeper: Can farm unlimited health/coins.
In-game footage
Seeds
PC 
0FYV B9EG (Planetarium adjacent to spawn)
PC D771 QQNR (Planetarium adjacent to spawn)
 Astrological Signs
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 The Binding of Isaac: Rebirth
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