summon Falling_block ~ ~2 ~ {Block:command_block,Data:1,TileEntityData:{Command:gamerule maxEntityCramming 24,TrackOutput:0b,auto:1},Time:1,Passengers:[{Block:command_block,Data:1,TileEntityData:{Command:scoreboard objectives add MECNearbyMobs dummy,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:command_block,Data:1,TileEntityData:{Command:scoreboard players set #Max MECNearbyMobs 24,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:command_block,Data:1,TileEntityData:{Command:tellraw @a {"text":"Use ``/gamerule maxEntityCramming #'' to change value.","color":"gray"},TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:repeating_command_block,Data:1,TileEntityData:{Command:gamerule maxEntityCramming,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:stats block ~ ~-1 ~ set QueryResult #Max MECNearbyMobs,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:stats entity @e[tag=!MECLivingMob,team=!NonExistantTeamBecauseItsNameIsTooLong,type=!Armor_Stand] set AffectedEntities @e[c=1,r=1,tag=MECLivingMob] MECNearbyMobs,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:scoreboard players tag @e[tag=!MECLivingMob,team=!NonExistantTeamBecauseItsNameIsTooLong,type=!Armor_Stand] add MECLivingMob,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:scoreboard players set @e[tag=MECLivingMob] MECNearbyMobs 0,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:execute @e[tag=MECLivingMob,score_MECNearbyMobs_min=0] ~ ~ ~ scoreboard players remove @e[r=1,tag=MECLivingMob] MECNearbyMobs 1,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:scoreboard players operation @e[tag=MECLivingMob] MECNearbyMobs -= #Max MECNearbyMobs,TrackOutput:0b,auto:1},Time:1,id:Falling_block,Passengers:[{Block:chain_command_block,Data:1,TileEntityData:{Command:execute @e[tag=MECLivingMob,score_MECNearbyMobs_min=1] ~ ~ ~ effect @e[tag=MECLivingMob,r=1] wither 2 0 true,TrackOutput:0b,auto:1},Time:1,id:Falling_block}]}]}]}]}]}]}]}]}]}]}]}