I am trying to figure out for a mechanism that will let me send a flow of villagers, or 2-tall/1-wide hostile mobs down a stream, reach a throttle point, then push a button to release exactly ONE of them down the continuation of the stream.
I thought this would be easy and very common... but I have not been able to find a single example. I've seen several mechanisms where the villagers pass through a stream and trapdoors open if none is present below (detected by a tripwire), but nothing that is straight horizontal, where they are held unless you push a button to let one through.
Does anyone know of at least one such design? If yes, could you post a link?