Tutorials/Guardian farming

In snapshot 14w25a, the new mob Guardian was added, which only spawns in the also newly added Ocean Monuments. It is possible to farm them for their drops of Raw Fish, Prismarine Shards, and Prismarine Crystals, which can be used to craft Prismarine variants and Sea Lanterns.

Spawning
Guardians only spawn in Ocean Monuments, which themselves only spawn in Deep Ocean biomes. They spawn within a 9-block radius of these monuments in any direction. The spawning area covers the top of the monuments (the decorative part on the very top with Sea Lanterns), to the base of the Prismarine Brick pillars. Building the farm under the main building where the pillars are is generally the easiest place, as the gaps between the pillars can be blocked off and Sponges used to clear the area of water.

Farming
As the guardian is a new mob, not many farming methods have been developed. Some farming methods are listed below:

Iron Golems
One of them is the Iron Golem method, where Guardians spawn and are funnelled using water currents to a trench filled with Iron Golems. As the Iron Golems attack the Guardians, the drops are collected using Hoppers and deposited in Chests. This method is fairly iron-heavy, due to all of the Iron Golems, which will need to be periodically replaced due to the Guardian's spike damage, and the large amount of Hoppers used. This video shows the working of the farm.

Super-efficient farm
Another farm is the 'OP', or super-efficient farm. This farm is very expensive to build in Survival mode, due to the amount of materials used, but produces over 100,000 items per hour. This video shows the working.