Stacked square mob farm

wattles' beginner mob farm, and the most-watched thing in the library at 1.8 million views. Stacked square platforms with 3x3 gaps, and mobs simply wander off the trapdoors on their own into a central drop tube, so there is no redstone, no dispensers and no clock anywhere in it. A slab and fence gate chamber at the bottom lets you kill them by hand for XP or leave it automatic. It is customisable for spiders and creepers and it is one of the few designs here that genuinely works on both editions.

• The platform is 13x13, not the 11x11 wattles says. Four blocks out each way from the centre gives 13, and this is the most repeated correction on the video by a wide margin.
• The design needs mobs to wander off the trapdoors, which only happens within 32 blocks of the player. Past the fourth layer you have to raise the AFK spot as well or the upper layers contribute nothing.
• Creepers can see you through the kill window and blow the base out. Put slabs over the hoppers with trapdoors where the slabs were, or build the bottom from obsidian.
• For XP specifically, use a sword without Looting. Armour a mob spawns wearing adds XP only if it is not dropped, and Looting makes it drop.
• On Bedrock, carpets and slabs do not stop spiders spawning, so use buttons. Rates there are far lower than on Java.
• Do not build it over a river or a mushroom island. Nothing spawns in either, which several builders found out the hard way.