You create mobs and execute commands. You need to edit the file multiblockmobs.mbm. Here are two examples of how to set up the file. You should place the soul chassis somewhere in the multiblock structure, but you do not need to include it in the multiblock structure file, which means it will not be removed. If your game crashes on startup, you have corrupted the file. Everything must be exactly as shown below, the spaces between the equal signs must be the same, you must have quotes, etc. Do not add or remove spaces between characters!
#Dimension
#Hashtags are comments
#X goes across, Y goes down
#Spacing is important
#Mob 1
!startMultiblockMob
!startDim
Dimensions:[x = 3, y = 3, z = 2]
!endDim
!startInit
minecraft:hay_block = "w"
minecraft:bone_block = "p"
multiblockmobs:soul_chassis = "s"
minecraft:air = "~"
minecraft:gold_block = "g"
!endInit
!startLoc
#z=0
["~s~"]
["wpw"]
["~p~"]
#z=1
["ggg"]
["ggg"]
["ggg"]
!endLoc
!startCustom
particals = "true"
particaltype = "modid:partical"
music = "true"
musicFile = "music"
soundEffect = "true"
soundEffectFile = "sound_effect"
customChat = "true"
customChat = "You made a mistake"
customCommand = "say Hi"
!stopCustom
!entityStart
entity = "harvestersnight:harvester"
!entityStop
!endMultiblockMob
!startMultiblockMob
!startDim
Dimensions:[x = 3, y = 2, z = 1]
!endDim
!startInit
minecraft:wool = "w"
minecraft:stone = "c"
multiblockmobs:soul_chassis = "s"
minecraft:air = "~"
!endInit
!startLoc
#z=0
["www"]
["c~c"]
!endLoc
!startCustom
particals = "true"
particaltype = "modid:partical"
musicBoolean = "true"
musicFile = "music"
soundEffectBoolean = "true"
soundEffectFile = "sound_effect"
customChat = "true"
customChat = "You made a mistake"
!stopCustom
!entityStart
entity = "minecraft:sheep"
!entityStop
!endMultiblockMob


