This command (which I made myself) summons THE BLOODSHEDDER BOSS (see my comment for the picture)
The original command is in the box; the updated version here (I hand-wrote the updated version):
/summon minecraft:wither_skeleton ~ ~1 ~ {CustomName:Bloodshedder,CustomNameVisible:1,PersistenceRequired:1b,CanPickUpLoot:0b,Health:40,Fire:1277951,Attributes:[{Name:"generic.followRange",Base:250},{Name:"generic.knockbackResistance",Base:0.75f},{Name:"generic.movementSpeed",Base:0.55f},{Name:"generic.attackDamage",Base:13}],Silent:1,HandItems:[{id:"minecraft:iron_sword",tag:{display:{Name:"Bloodshedder's
sword",Lore:["Poisonous"]},ench:[{id:16,lvl:2},{id:18,lvl:3},{id:20,lvl:2}]},Count:1},{id:"minecraft:shield",tag:{display:{Name:"Bloodshedder's
shield",Lore:["Made of pure","darkness."]},
BlockEntityTag:{Patterns:[{Color:1,Pattern:"sku"},{Color:1,Pattern:"tts"},{Color:1,Pattern:"bts"},{Color:14,Pattern:"gru"}]},ench:[{id:0,lvl:2},{id:7,lvl:3},{id:70,lvl:1}]},Count:1}],HandDropChances:[99F,99F],ArmorItems:[{tag:{display:{Name:"Bloodshedder's
Boots of
silence",color:14355725},ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]},Count:1,id:"minecraft:leather_boots"},{tag:{display:{Name:"Bloodshedder's
leggings",Lore:["They are wet...","with
blood."],color:0},ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]},Count:1,id:"minecraft:leather_leggings"},{tag:{display:{Name:"Bloodshedder's
Cloak",color:14552333},ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]},Count:1,id:"minecraft:leather_chestplate"},{id:"minecraft:skull",Damage:3,tag:{SkullOwner:Bloodsheds,display:{Name:"Bloodshedders's head",Lore:["Use as a trophy",""for defeating the","Bloodshedder."]}},Count:1}],ArmorDropChances:[99F,99F,99F,99F],ActiveEffects:[{Id:7,Amplifier:1,Duration:100,Passengers:[{id:"minecraft:armor_stand",Passengers:[{id:"minecraft:falling_block",NoGravity:1,Block:"minecraft:always_active_command_block",Time:-2147483648,Command:"execute
@e ~ ~1 ~ [r=130,tag=blood] ~ ~ ~ summon area_effect_cloud ~ ~1 ~
{Particle:largesmoke}",Passengers:[{id:"minecraft:redstone_block",Time:-2147483648,DropItem:0,HurtEntities:0,Passengers:[{id:"minecraft:wither",Invul:900,ActiveEffects:[{Id:7,Amplifier:1,Duration:2147483647}]}]}]}]}]}]}
There is currently a bug that does not let you get the Bloodshedder's drops, so after you kill the Bloodshedder, do these commands (it's just cheating if you do them before you defeat the Bloodshedder)
Bloodshedder's shield:
/give @p minecraft:shield 1 0 {display:{Name:"Bloodshedder's shield",Lore:[Made of pure,darkness.]},BlockEntityTag:{Patterns:[{Color:1,Pattern:"sku"},{Color:1,Pattern:"tts"},{Color:1,Pattern:"bts"},{Color:14,Pattern:"gru"}]},ench:[{id:34,lvl:3},{id:0,lvl:2},{id:70,lvl:1}]}
Sword:
/give @p minecraft:iron_sword 1 0 {display:{Name:"Bloodshedder's sword",Lore:["Poisonous"]},ench:[{id:16,lvl:2},{id:18,lvl:3},{id:20,lvl:2}]}
Head:
/give @p minecraft:skull 1 3 {SkullOwner:"Bloodsheds",display:{Name:"Bloodshedder's head",Lore:["Use as a trophy","for defeating the",Bloodshedder]}}
Cloak:
/give @p minecraft:leather_chestplate 1 0 {Unbreakable:1,display:{Name:"Bloodshedder's Cloak",color:14552333},ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]}
Leggings:
/give @p minecraft:leather_leggings 1 0 {Unbreakable:1,display:{Name:"Bloodshedder's leggings",color:0},Lore:["They are wet...","with blood."],ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]}
Boots:
/give
@p minecraft:leather_boots 1 0 {Unbreakable:1,display:{Name:"Bloodshedder's Boots of
silence",color:14355725},ench:[{id:0,lvl:2},{id:1,lvl:4},{id:7,lvl:3}]}
Warning: this boss is QUITE powerful, since it's sword gives both the Wither effect and flame at the same time. I got the idea for this boss from one of NightFang's YouTube channels, called Bloodsheds.