@Zabolca omg! i didnt know that! i will never auto farm potatoes and carrots again....

It was kind of a pain in the ass to collect it all but it's definitely worth it. :)

Thanks to a little inspiration from BoneChi11er I redecorated the prison:

This my guardian farm. I didnt destroy the outer structure. I just hollowed the inside:

This is the inside, the spawning area:

This is the auto killing chamber for the item grinder mode:

For the xp mode, I made a auto toggle able nether portal (see the lamp above, if they light up then its xp time) before the guardian drops in the killing chamber. The guardians are then transported to the nether for a second lava chamber that is enough to kill them by a single potion of harming:

In a really good spawn rate, 100+ mobs is easily reached in less than 2 mins.