Minecraft wiki entry for Guardian_farming, associated text: While manual kill designs are possible, keep in mind that the Guardians' natural thorns damage will damage players using swords rather than arrows or damaging potions, and that guardians can fit through 1-block holes (thus attacking from above or around a slab or other small gap is needed to prevent escapees). A manual-kill Guardian farm should thus provide for healing, either a beacon providing regeneration or potions. Having a health of 30 × 15, Guardians will require a 34-block drop to kill. Lava over a 12-block drop is sufficient to kill with a combination of fall, lava, and fire damage.