No cats creeper farm

Water flushed creeper farm over deep ocean, with no cats and no snow golems. Creepers spawn on stacked platforms, dispensers flush each platform with water on a repeater clock, and the current carries them off the edge onto carpets and hoppers below. Nothing has to be tamed, brought or kept alive, which is why it costs far more blocks than the cat and golem designs but needs no upkeep once it runs. Java only, the water system does not work on Bedrock. The AFK room decides whether it works at all, and the height given in the video is wrong.

The AFK height in the video is wrong. At Y200 the creepers despawn about six blocks above the hoppers and you get nothing at all. Y190 is what most builders settle on, and one confirmed it with MiniHUD despawn spheres.
Place every trapdoor and fill every dispenser before you put the roof on. Doing it afterwards means working in the dark with mobs spawning all around you.
Light the whole area before you start. One builder had four finished layers blown up.
The 9000 figure needs three or four separate copies of this farm, eight layers each. That is in the description and never in the video, and the creator has acknowledged the complaint.
On Bedrock the water system does not work. One builder swapped it for a nametagged cat penned in with trapdoors and got it running, slower.
Bring spares. You lose glass without silk touch and misplace things simply because of the quantities involved.