[Technical] Changes from Vanilla Minecraft

Anvil Changes

• Renaming an item has a fixed cost of 5 levels.
  • If you want to rename a stack of items, that costs 5 levels + 1 per stacked item, up to a maximum of 15 levels.
• When combining multiple items, renaming is free.
• Although Vanilla Minecraft has a cap of level 39 for anvil usage, EMC will allow you to go over this limit by reducing the cost of all enchantments over the cap to 39 levels.

[Source]

Entity Activation Range

• Mobs, animals & items that are not in water are frozen if you're not within the following amount of blocks from them:
  • Town: 12 blocks for animals, 16 blocks for mobs
  • Wild: 12 blocks for animals, 32 blocks for mobs
  • Nether: 12 blocks for animals, 32 blocks for mobs
  • End: 12 blocks for animals, 32 blocks for mobs.
  • Wastelands: Currently unknown. Presumed to be the same as the wild.
• Items in water are not affected by these ranges, and should still move provided that chunk would be loaded in vanilla Minecraft.
• Things such as crop growth on farms are not affected by this.
• Only the X and Z axis' are checked, there is no Y axis check (meaning mobs above and below you are affected by this)
  • Note: Vanilla also has similar logic as this for monsters at 32 distance. So movement logic for monsters is essentially unaffected. However, Vanilla's logic also includes a Y distance. This Vanilla logic is planned to be removed so natural spawn grinders will function better.
• The following things are immune to Entity Activation Range:
  • Sheep missing wool
  • Animals/mobs that:
    • Aggressive to another entity
    • are on fire
    • are riding in a vehicle
    • are in a vehicle with a passenger
    • are not on the ground
    • have special effects
    • are a baby
    • are in love

Entity Limits

• SMP Town:
  • You can have up to 100 animals per residence.
  • There is no limit on other entities, such as paintings and dropped items.
• Utopia Town:
  • You can have up to 150 animals per residence.
  • There is no limit on other entities, such as paintings and dropped items.
• Wild/Wastelands (All Servers):
  • Is measured in a 64 block radius around you.
  • There is a limit of 250 mobs in this area. This is spread across animals and monsters.
  • There is no limit on other entities, such as paintings and dropped items.
  • The mobs are not per player. They are per area - meaning another player can put an area up to it's cap it they're very close to you.
• Use the command /entc to see the amount of mobs in your current area.
  

View Distance

• EMC's View Distance is 7
• View distance is the amount of chunks that is sent to your client - it essentially caps your render distance.

[Source]

Mob Spawning Distance

• In Vanilla Minecraft, mobs can spawn up to 128 blocks away from you.
• In EMC, mobs can spawn up to 64 blocks away from you.

Mob Spawning Limits & Density Checks

• In Vanilla Minecraft, the formula to calculate how many mobs can spawn is 70 * amount of chunks available under Mob Spawning Distance (these limits are per player).
• In EMC, the formula to calculate how many mobs can spawn is the same - however there is a cap of 90 mobs (this limit is per player).
  • If there are under 90 mobs in the area, it checks that there aren't too many of that mob in the current area.
    • Mobs are limited to spawning in clusters of 2.
    • A cluster size is 20 blocks X/Z, and 16 Y.
    • If there are 2 monsters within the cluster of where an entity is trying to spawn, the spawn will be cancelled.
  • Natural spawning will continue until every player has 90 monsters in their range.

Mob Despawning / Auto Kill

• Monsters will despawn instantly within 15 seconds if they are further than 64 blocks from a player, in X/Y/Z (The check is a 64x64 cube, not 3D distance)
  • Monsters that have picked up another players items will not despawn
• If an area exceeds entity limits by any means (by logic cases that can not be prevented such as 2 players being near each other and loading chunks full of monsters that push them over, or monsters moving into rage), the system will automatically kill entities until it is at the limit
  • Monsters are targetted first before animals/villagers
  • Withers are immune
  • Monsters that have picked up players items WILL be immune (bug: EMC-24)

Mob Spawning Light Limits

• EMC does not change the light limits that mobs spawn in using custom code. However, it is suspected that a Spigot bug may cause mobs to spawn in lit up areas.
• It's possible that chunks have invalid light data, allowing mobs to spawn in lit areas. This is also a bug, but will be fixed by an automated system eventually.

Mob AI Changes

• Zombies break doors even on normal difficulty (Coming soon to EMC)

Oh cool, good to know

Thanks

Im not really sure about this one. I asked aikar once and he said 5 chunks away from the player but i believe that he corrected himself and said it was 4 chunks. Also in vanilla its a 128 block radius, not a square I believe. Please correct me if I am wrong

Great job Jack, very useful

It's 5 chunks, not 7 - so we've both got it wrong.
However, he's included vanilla's - which is 8 chunks.

The 128 block radius I am SURE about, because any mob 128 blocks away from the player are automatically despawned. This is verified in the wiki. http://www.minecraftwiki.net/wiki/Spawn#Despawning

I found it

Hrm. Will correct that then, and ask Aikar about it.

EDIT: Thanks for finding that for me.

Jack... always making guides... I got a career for you

so does this include iron doors or just wooden ones?
P.s. sorry about the bump

It's in Official Guides, so bumps don't really matter.

It's only wooden ones.

So That's why enraged mobs can see you from so far away...

Oh god no.... Zombies will be able to break down doors on normal difficulty?

So what happened to the 32 block proximity detection range? Y was always affected by this... meaning if you are 33 or more blocks above a mob they stop moving... if you are standing right above where a mob is - and it's 32 they will start moving again...

Bump, just in case some new changes have happened (and I have noticed aincrease in interest about how EMC has changed mobs/spawning).

They would of made a new thread.

Not always, thats why we now have the small updates thread.

True, sorry jkjkjk wasn't trying to be rude was only pointing out which probably wasn't necessary

It is was stickied (the page I found it on said it was, and I didn't think to check if it still was). But besides that, IMO, it wouldn't make sense for them to make a new thread since this one is already structured so well.
Edit:

No problem, there was just a lot of debating about ghast spawning today, and I recently found this again. Horrible time to bump it though.

The way I read this is that it was planned to remove the 32 distance in the Y. Does anyone know if this was actually done?