The Gadderhammer is a two-handed members-only maul. There are no combat requirements for wielding the gadderhammer. To obtain the gadderhammer the player must defeat Gadderanks during In Aid of the Myreque. Even though you can buy it from another player, you cannot wield it until you defeat Gadderanks.
This weapon cannot be made using the Smithing skill. It has a very similar appearance and combat animation to the granite maul.
If lost, the Gadderhammer can be bought from the Burgh de Rott general store owner for 3,000 coins.
The Gadderhammer does extra damage against Shades similar to the Keris versus Kalphites, possessing a 25% damage bonus against Shades as well as a 5% chance to deal 2x damage.