Oddfelt

Oddfelt is General Viggo's loyal valet, who is always armed with a razor rimmed bowler hat.

He needs to be defeated in a firefight with Chang on the Secret Island, as the firefox tries to prevent being suffocated in Viggo's Vault. He is in charge of protecting the final key, and is thus the final mini boss you encounter in the vault.

Like with the other mini bosses found in the vault, you have a total of 60 seconds to defeat him.

Strategy
He uses his bowler hat frequently as a weapon. He will attack from a distance, lunging it across the room to attack you. There will be a bit of a pause as he reaches for his hat, so use this to your advantage.

The best way to defeat him is the same as the others - Shoot from a distance, and try to trap him against the cage walls. If you're low on ammo by this point, try using powerful weapons such as a Cluster Bomber to wane his health away.

Once defeated, he will give up Cage Key 4, and you will finally be allowed to exit the vault once the final button has been pressed down.

Trivia

 * Oddfelt is a parody of the James Bond villian Oddjob. This is reflected in his appearance and method of attack, using his bowler hat.
 * If Oddfelt is defeated using the Flame Gun or Flamethrower, he will become invincible. His body will be burnt away, but his hat will remain and he will continue to attack and move as though he were still alive.