Before you decide to travel to the Central Island, south of the Azimuth to obtain the Magma staff, you will need to make some preparations and achieve some prerequisites before attempting to obtain the staff.
The staff is important because it is required to open the entrance to Diggery Poker.
Preparations
Players will have to travel to the entrance to Crocodilopolis to obtain Zenithian armor before attempting to get the Magma staff in Dragon Quest V. The armor is located in one of the side rooms, but will be unobtainable without a key.
In order to get the Ultimate Key, you must defeat Bjorn the Behemoose.

Bjorn’s Attributes:
4,700 HP
244 MP
300 Attack
150 Defense
75 Agility
9,500 Experience
Bjorn is located in La Guardia. Upon defeating Bjorn, you will receive the Ultimate Key and could proceed to the entrance to Crocodilopolis to get the Zenithian armor.
There are a couple of buffs that you should be aware of when starting to battle Bjorn. If you have the Zenithian Sword, you can use it to nullify his buffs. This is highly recommended if you are struggling to defeat him.

Before attempting to defeat Bjorn, you should reach level 24 and have many of your partners at level 20 or higher. Hocus Pocus can be used to help revive your partners during the battle.
Staff Attributes (The Magma Staff)
The Magma Staff in Dragon Quest V has an attack bonus of 63. The Magma Staff is also capable of casting “Bang!”.
Bang costs 5 MP and delivers all enemies with approximately 30 damage. This mirrors the effects that came from the Magma Staff in Dragon Quest IV.
The only way to open the Diggery Pokery is to obtain the Magma Staff.
Finding the Magma Staff
You should start your journey traveling to the Zenithian Tower. Along your journey, step inside of the Stairway to Zenithia. Travel to the top of the tower, and visit the top platform where you will receive your award, the Magma staff, and receive further instructions!

Upon retrieving the magma staff, make your way to the south of Lofty Peak. You should travel to Gotha and fly on a northbound trajectory until you get to the cave location.
The cave location is surrounded by a body of water, as seen in the image.

You can use the magma staff at the entrance once it is in your inventory to proceed.
In order to use the staff, open your inventory and blow open the cave entrance. This will allow you to proceed into the cave and continue with the story.
