Betrayer's Shield
Generates a protective shield upon reload. Blockner lost his knighthood when he betrayed Ser Manuel, but he did not lose his gun. He did that much later.
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Betrayer's Shield is a gun . Upon reloading, it leaves a protective shield on the ground, which blocks enemy bullets (but not the player's). Only one such shield can exist at any time. The shield is destroyed after taking too much damage or upon leaving the room.
Synergies
If the player has 
Lies , Betrayer's Shield gains infinite ammo, a much larger magazine size, increased accuracy, and extremely high fire rate. Like other guns with infinite ammo, it cannot reveal secret rooms.
Betrayer's Lies can be combined with other guns using 
Duct Tape by dropping Lies, using Duct Tape, and picking up Lies again.
However, using Duct Tape with a beam weapon such as 
Disintegrator will cause it to eventually run out of ammo. It can be refilled by simply dropping it and picking it up again.
Notes
- The Betrayer's Shield is peculiarly a member of the PISTOL gun class despite almost certainly being more at home among the members of the FULLAUTO class.
- There are a few bullet patterns in certain boss fights that the shield will not block, such as the large bullets that the Cannonbalrog shoots when he disappears and the line of bullets that spins around the Resourceful Rat in his first phase.
Unlock Method
Kill 
Blockner , and talk to 
Ser Manuel in the Hall of Knowledge .