The following rule has been added to our rules list:
Darkroom spawners using autokill mechanisms or water flushing to push mobs off of spawning pads are not allowed anywhere.
...After some discussion in our last meeting, this rule was added both to make clear what is forbidden and to relax some confusion on what some thought to be forbidden. Here is a quick Q & A to hopefully address what it means.
"What is meant by autokill?"
"Autokill" means that you use drowning, cactus, mob-triggered suffocation methods, potion dispensers, or any other automated method to kill mobs. This primarily pertains to systems that use hoppers or an item collection point. An autokill system in dark rooms that uses cactuses to destroy mobs AND items is acceptable. Otherwise, you need to deliver the final killing blow, yourself.
"Darkroom Spawners can't have autokill. Does that mean other spawners can?"
Yes. We will allow autokilling for all crate spawners, pigman farms and slime farms, guardian farms and witch hut spawners as long as they don't have a darkroom attached to them. We only forbid autokilling with dark room spawners. A good rule of thumb is this: If you can regularly get creepers and enderman, it's probably not OK.
"But I thought those other types of auto-kill spawners weren't allowed either?"
There has been some confusion about this in the past. We clarified it with Raid during our last meeting and they are fine to have. Sorry about that!
"What is meant by water flushing?"
I hope this one is self-explanatory. This refers to systems where water moves mobs off of the spawning area and into the killing zone, usually done with dispensers or piston-blocked water tiles. Water that is already moving and doesn't need to be started and stopped is fine, but remember that mobs won't spawn in it. Water also is still fine for elevators or moving mobs along the bottom of the spawner. In practice, we are attempting to avoid mob-triggered systems where a large area of waterflow is constantly being turned on and off. This is bad for us.
"So then what kind of mechanism is legal for darkroom spawners?"
We allow dark room spawners that utilize tripwire hooks and pistons that push the mobs off. We have found this puts far less strain on the server tick rate.
We strongly prefer you build your dark room spawners with an "off switch." This can be done with redstone lamps to make it a "not so dark" room or just by extending all of the pistons while not in use. We will not ban you just for not having one, but if it becomes an issue, we may ask you to implement it to keep mobs from accumulating while not in use, so save yourself some work and do it right the first time!