@TheForgotten20 this is ez to solve, instead of making a 1x1 kill zone, make it 1*x, e.g. 1*5 .. this gives them walking room and from object collision they will automatically spread out

Mobs also tend to bunch up in the corners, so a 2x2 will actually fit more than a 1x4. a 2x2 should also be plenty for 100 mobs (i.e. server limit) so there's no need to go any bigger.

They won't change the colour of their coat but can change all their trades. So if you have a librarian with a shitty book trade, or a farmer with a crap pumpkin one you can serve him up to the zombies to try for better trades.

It sets how many mobs (also players) can be in a 1x1 space before they "crush" each other to death.
With the default of 24 you can have up to 25 mobs in a 1x1 safely (each one collides with 24 others)
If you have 26 mobs they will all take suffocation damage until one dies.

Gamerule is great for increasing performance because it can save the game having to calculate too many collisions. The choice of 24 for the default seems a bit odd to some

They do still spawn naturally, but like you said in your first post you're less likely to get librarians than ever before (also make sure not to build it in a desert). Remember you can still infect and cure villagers to get the trades you want - particularly useful with librarians now they're so rare.

I think you've come across a slightly unexpected product of the changes to entity IDs, zombie villagers and zombies now have separate IDs (hence separate spawn eggs) so a zombie spawner can't spawn zombie villagers any more :(

I do remember at one point in 1.9/1.10 you could find spawners with a zombie villager in (purely cosmetic). I don't think these exist any more for the same reason though. No more villager spawners, get breeding!!

Very cool design, and the video shows it off excellently too.

I was wondering if it would be worthwhile having two separate killing chambers alternating the water. As you have it the shulkers only have somewhere to tp to half the time, so you're likely to reach the spawner cap while the water is dispensed. It's probably totally unnecessary but I thought I'd mention it anyway.

So this is the Team Eye mascot right?

@_Drachenzorn_ Clearing an ocean? You can also do this:
https://www.youtube.com/watch?v=ODWGasI4f-k

Ahem:

Please, please, please if anyone builds this keep it fairly small and use a slower engine than in the video if you know how. You'll hurt the poor server otherwise.

@R4iscool1 #3 and #4 would be allowed.

#1 & #2 maybe depends.

I assume this was aimed at my list, thanks! Any chance of some clarification on the first two I listed?

@Tez1010 Anything like this will work nicely (replace the bottom middle slab with a daylight sensor and the bottom side ones with any immovable blocks and you can do away with the bottom pistons)

If you feel the need for speed you can't beat the old right click minecart elevator

If you want something a little more fun you could try something like this:

(Note design showed here no longer works. I do know of an alternative that has the same effect, gimme a shout if you're interested)