Most Important: First make sure the Their Master's Voice World Change is active by talking to the town Guides ( location of all guides - thank you Zupakode ) by the ships in most towns
Player: Hi
Guide: Welcome Player ....
Player: Master voice
Guide: The strange tower with the servants on Edron is covered in slime
EDIT: to include Player and Guide conversation
Second Most Important: Be sure someone/team is not currently doing it
For the Mad Mage from Their Master's Voice World Change you need to talk to the NPC and take the slime gobbler from it. Then proceed down two floors to the main floor and use the Slime gobbler on the Slime fungus (they all look a little different) which you can do once every 5 seconds. Either you or your team need to 'gobble' all 350 slime, with everyone needing to have 'gobbled' at least 25 to participate in next stage of this World Change.
Then the Iron, Golden (best loot, hope to have a Golden can of oil drop) and Diamond Servant's will appear. Ive only done this solo and the numbers listed on the wiki sound about right (roughly) of about 250 Iron, 200 Golden and 60 Diamond (Hope to loot a . Be careful if you're a lower level soloing because they can surround you in large numbers easily. They come in waves so you need to clear them all and then they will respawn, so think about where you are when you kill the last one so you dont get a big spawn on top of you.
When you've killed all the Servants, the Mad Mage will spawn in one of these locations
Kill him and take his loot and the Fungus respawns