Moon Rabbit 0.2
From the moon... It's very fast but weak. 

Tags: Rabbit;Weak;Fast;Moon;Alien
Difficulty: Normal

Copy the Code and put in Command Block (if you find some bug please report in comments):

/summon Rabbit ~ ~1 ~ {CustomName:"Moon Rabbit",CustomNameVisible:1,RabbitType:99,Equipment:[{id:glowstone_dust,Count:1,tag:{HideFlags:31,AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"generic.maxHealth",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872},{AttributeName:"generic.movementSpeed",Name:"generic.movementSpeed",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872},{AttributeName:"generic.attackDamage",Name:"generic.attackDamage",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872}],display:{Name:Moon Dust,Lore:[From the Moon....]}}},{},{},{},{}],DropChances:[2.0F,0.085F,0.085F,0.085F,0.085F],Attributes:[{Name:generic.movementSpeed,Base:0.1},{Name:generic.attackDamage,Base:30},{Name:generic.followRange,Base:100},{Name:generic.knockbackResistance,Base:0}],HealF:100}/summon Rabbit ~ ~1 ~ {CustomName:"Moon Rabbit",CustomNameVisible:1,RabbitType:99,Equipment:[{id:glowstone_dust,Count:1,tag:{HideFlags:31,AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"generic.maxHealth",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872},{AttributeName:"generic.movementSpeed",Name:"generic.movementSpeed",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872},{AttributeName:"generic.attackDamage",Name:"generic.attackDamage",Amount:10,Operation:2,UUIDLeast:894654,UUIDMost:2872}],display:{Name:Moon Dust,Lore:[From the Moon....]}}},{},{},{},{}],DropChances:[2.0F,0.085F,0.085F,0.085F,0.085F],Attributes:[{Name:generic.movementSpeed,Base:0.1},{Name:generic.attackDamage,Base:30},{Name:generic.followRange,Base:100},{Name:generic.knockbackResistance,Base:0}],HealF:100}

Hades 0.3
The God of Hell!!! Yes it's possible kill him. Fire Attacks not so effective to him. 

Tags: Zombie;Enchanted Golden Armor; 100 <3; Enchanted Blaze Rod.
Difficulty: Hard

Copy the Code and put in Command Block (if you find some bug please report in comments):

/summon Zombie ~ ~1 ~ {CustomName:"Hades",CustomNameVisible:1,CanBreakDoors:1,Equipment:[{id:gold_sword,Damage:20,Count:1,tag:{Unbreakable:1,display:{Name:Hades Cube,Lore:[§4The Legenday Cube of Hades...]},ench:[{id:16,lvl:2},{id:19,lvl:10},{id:20,lvl:10},{id:34,lvl:1}]}},{id:golden_boots,Count:1,tag:{display:{Name:Hades Boots},ench:[{id:1,lvl:10}]}},{id:golden_leggings,Count:1,tag:{display:{Name:Hades Leggings},ench:[{id:1,lvl:10}]}},{id:golden_chestplate,Count:1,tag:{display:{Name:Hades Chestplate},ench:[{id:1,lvl:10}]}},{id:skull,Damage:3,Count:1,tag:{display:{Name:Hades Head},SkullOwner:MHF_Blaze}}],DropChances:[2.0F,2.0F,2.0F,2.0F,2.0F],Attributes:[{Name:generic.maxHealth,Base:200},{Name:generic.movementSpeed,Base:0.5},{Name:zombie.spawnReinforcements,Base:1.0F},{Name:generic.attackDamage,Base:30},{Name:generic.followRange,Base:100},{Name:generic.knockbackResistance,Base:0}],HealF:200}