• Guns simultaneously shoot forwards and backwards. The backwards firing shots will be significantly less accurate.

• Gruber's Bane - If player also has [Shadow Bullets] all backward shots have an additional projectile.
• Like Shooting Fish - If the player has [Barrel] , a fish pops out of the [Barrel] and fires bullets. The last shot of each magazine fires fish who flop around on the ground and fire at enemies.
• Interacts strangely with Double Vision - Instead of doubling the backwards shots, a player that activates [Double Vision] with Backup Gun equipped will fire three shots forwards, and one shot backwards.
• With Backup Gun, [Dark Marker] 's charged shot's accuracy is decreased, which can cause it to fail as the two projectiles have a chance to miss each other.
• Negates the recoil of the [Mutation] and the [Grasschopper] .
• Synergizes extremely well with weapons that can bounce shots on walls or release homing projectiles such as [The Scrambler] , the [Bee Hive] or the [Moonscraper] .
• Works well with [Orbital Bullets] , as shots fired backwards which would normally miss will instead orbit the player.
• For some reason, Backup Gun seems to cause the forward shot of the [Prize Pistol] to be inaccurate. It's recommended to drop the item in the room before speaking to [Winchester] to start the game, although it's possible to drop it during the game by backing up to a wall.
• The backward shot originates from the front of the gun, in the same pixel as the forward shot. This works well with extremely close range weapons, like [Blasphemy] and [Quad Laser] , and weapons with very large bullets.
• With the [Alien Engine] , the gun will also fire an invisible flame backwards, though recoil is not affected.
• Does not affect [Composite Gun] 's charged shots.
• Does not affect the [Zorgun] 's final shot.
• The backwards shots can trigger the multi-shot effect of the Y.V. shrine .
• [Chance Bullets] triggers independently for forwards- and backwards-firing rounds.
• Guns that fire forwards and backwards at the same time like the [Directional Pad] and [Face Melter] have their damage doubled.

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