Annabelle

The Anabelle Shotgun is a weapon used by Father Grigori in Ravenholm. The Anabelle uses .357 Magnum Rounds, which makes it clear why this weapon is so powerful.

The Anabelle can fire 2 shots before having to be reloaded. The player is not intended to use the Anabelle, but, in Garry's Mod, a HL2 game modification, the player can spawn an npc weilding the weapon, and can kill that npc to pick up the gun. There is no view model for the Anabelle, therefor it takes the form of the SPAS-12 shotgun. It fires rather slowly, and houses only 2 rounds at a time.

Tactics
Father Grigori is the only npc that uses the Anabelle. In normal combat, Grigori uses the weapon with great accuracy, and is skilled at shooting at a zombie's head. Thanks to Grigori's npc scripts, he rarely misses a Zombie's head.

The Anabelle can only house 2 rounds at a time (mentioned above), so Grigori has to reload frequently. This can be a problem when facing a large number of zombies. Therefor, leaving Grigori to kill all the zombies himself will result in him being overwhelmed.

Trivia
In Half Life 2, because Father Grigori can be killed, the player can pick up the Anabelle, but can only use it briefly as the screen fades to black when Grigori dies.