Anvil is a transformation of Conker's from a few B Pads in Conker's Bad Fur Day and Conker: Live & Reloaded. It temporarily turns Conker a black anvil. As an Anvil, Conker slightly moves upward and quickly falls onto the B Pad. After his impact with the ground, Conker turns back to normal.
There are four instances where Conker transformed into an Anvil. The first time is by opening trapdoor in the entry room of Poo Cabin, where Conker can explore the rest of Poo Cabin from. The second time is when Conker goes off the diving board in Barn Boys, which opens a short pathway with Cash at the end.
The third instance is at the start of the Uga Buga chapter, where Conker slams a statue of a cat head. The statue goes down slightly, and Conker (as an Anvil) must hit it a few times until him and the statue fall a level below. There, Conker must slam the statue head again to open the pathway to the fiery cavern.