The Hag 1 is the weapon that Gruntilda uses in the final battle between her and Banjo and Kazooie in the video game; Banjo-Tooie. It's also known as the Monstrous Mechanical Mud-Muncher.
The Hag 1 is a giant tank with an enormous drill. It also contains lasers, two mortar cannons, able to spit out minions, and spew out poison gas.
Banjo-Kazooie: Grunty's Revenge
Though the Hag 1 doesn't appear Grunty's Revenge, it's been implied that after Mecha-Grunty was destroyed, Klungo, and Gruntilda's sister; Mingella, and Blobbelda uses the remaining parts to create the Hag 1.
Two Years after Gruntilda's defeat, and the completion of the Hag 1, Gruntilda's sister arrived with the Hag 1 to rescue their sister.
During the game, it was implied that the Hag 1 ran over the grey Jinjo house, which killed all of them and frighten all the other Jinjos.
When Banjo and Kazooie made it to the top of Cauldron Keep, they encountered Gruntilda inside the Hag 1. It has the highest hitpoint in the entire game; 100. Every time 10 hitpoints are taken away, the boss battle becomes more and more tougher to beat. Gruntilda will activate it's lasers, shoot out mortar cannons, attempt to ram Banjo and Kazooie, summon minions, and spew out poisonous gas. When the Hag 1 has only one hitpoint left, Gruntilda will start to unleash her most powerful spell. If Banjo attack her before she unleash one of her spells, she'll accidentally drop her spell inside the Hag 1 which causes both her and the Hag 1 to explode.