How to Find and Use Magma Cube Spawners in the New Halls
Where the Spawners Are
The overhaul adds stairs and wings to the interior halls, and these wings are where magma cube spawners generate. Unlike the blaze spawner, magma cube spawners are not guaranteed, so you may need to explore several fortress wings before finding one. Walk the full interior rather than just the main bridge. The new stair sections connect different levels, so check upper and lower floors of each wing.
Farming Magma Cream
Magma cubes drop magma cream, which is used for brewing fire resistance potions and crafting magma blocks. Larger magma cubes split into smaller ones when killed, so keep swinging until no cubes remain. A sword with Sweeping Edge helps clear the small cubes quickly. Because magma cubes bounce and can push you around, fight them in a corner or against a wall to avoid being knocked into lava or off a ledge.
Safety Around the Spawner
Magma cube spawners sit inside the fortress halls, which may also contain blazes or wither skeletons nearby. Clear the surrounding rooms before starting a farm. Do not break the spawner unless you are finished with it, since spawners cannot be obtained as items without a Silk Touch pickaxe. If you want to relocate the farm later, mark the coordinates so you can return.