Ok, so I was on Minecraft just and messing around with NBT data tags, and when you do /difficulty 1 and then /summon Slime ~ ~ ~ {Size:250}, it spawns it in the ground and makes the server be really laggy but the client still works fine. I got a screenshot of it.
MC-68451
Spawning a Slime with insane size is causing issues
Resolved
Won't Fix
1
Slimes can have one of three sizes, everything else is not supported.