Let's talk about the bosses first, there are 4 bosses each drop component needed to make ender eyes, yes ender eyes recipe have been replaced you don't have to hunt for enderman for ender eyes

Sea guardian

HP : 200
XP reward : 100
Attack type : melee only
Attack damage : 15

Weakness

The sea guardian will burn on daylight which can help you damage it

Loot

Sea guardian armor
Durability : 2000
Effect | amplifier
Mining fatigue | 1
Resistance | 4
Slowness | 1

Rebreather
Durability : 539
Effect | amplifier
Water breathing | 1

Shell (ender eyes component) 
Summon item:

Deactivated sea guardian

Recipe

Elder enderman

HP : 300
Xp reward : 150
Attack type : melee and summoner (summon 4 enderman minion every 10 second) 
Attack damage : 10 ( if direct hit)

Weakness

The elder enderman got hurt when wet

Loot

Cursed medallion
Durability : 1666
Effect | amplifier
Bad omen | 1
Blindness | 1
Health boost | 1
Mining fatigue | 1
Regeneration | 3
Weakness | 1
Elder ender blood (ender eyes component) 

Summon item :

Mysterious summoning book

Recipe

Magma king

HP : 300
Xp reward : 100
Attack type : melee and summoner (summon 2 magma cube every 5 second) 
Attack damage : 3

Weakness

Magma king got hurt when wet

Loot 

Magma sword
Damage : 10
Durability : 1000
Effect | amplifier 
Haste | 1
Speed | 1
Jump boost | 1 

Magma king fire (ender eyes component) 
Summon item :

Magma king core 

Recipe

Ghast mother

HP : 100
Xp reward : 100
Attack type : range (explosive) and summoner (summon 4 baby ghast after spawn once) 
Attack damage : 15 ( if direct hit)

Weakness

Slow moving and large target

Loot

Baby ghast 
Durability : 1000
Effect | amplifier
Slow falling | 1

Mother ghast eye (ender eyes component) 
Summon item :

Crying baby ghast doll

Recipe

Now you've beaten all the boss time to make ender eyes to beat ender dragon
First combine shell and elder ender blood to make infini ender

(infini ender work like ender pearl except it has unlimited throw ability and less affected by gravity) here the recipe

Then combine magma king fire with mother ghast eye to make fiery eye

Recipe

Crack the infini ender (if you don't wanna use it and instead use it to make ender eyes) like this

Combine both cracked infini ender and fiery eye, it will give 20 ender eyes
 

Other info
New mob : Baby ghast 
HP : 5
Xp reward : 0
Attack type : range (small fireball) 
Attack damage : 3

Enderman minion
HP : 20
Xp reward : 0
Attack type : melee
Attack damage : 7

Enderman will now drop a new type of ender pearl (but it's Identical to the original just different texture)

All mobs and item identifier start with ak:

This addon is still work in progress, it might have some bugs and things to change in the future

(The model picture above is now outdated
Look at update version 1.1 part for the new model)

Update
Version 1.1

All the other boss (except elder enderman ) model have been significantly improved here below is the new model and also sea guardian armor model also got changed
 

New trophy block dropped by the bosses to decorate your house
 

New death message, when a boss is defeated a message will be sent (like on Terraria) 
 

This update is a bit small update since I want to improve the base boss before adding more boss

Update version 1.5

This update added new bosses and structure to the bosses as well as few other improvement

New bosses

Just a note here the new bosses doesn't have weakness as of now, I may add it in the next update

The old one:

HP : 200(phase1) + 300(phase2) = 500
XP reward : 100
Attack type : melee only and area damage /melee and minion tormented souls (only phase2)
Attack damage : 10
Additional information: the old one have two phases, ghost of the old one(phase 1) and the true old one(phase2) the true old one, will be summoned after ghost of the old have been defeated
↓
Tormented souls

HP : 20
Attack type : melee
Attack damage : 3
 

Loot

Notch fedora

Durability: 456
Effect | amplifier
Village hero | 1
Can be repaired with emerald (fully repaired)

Steve shirt

Durability : 659
Effect | amplifier
Haste | 2
Strength | 1
Can be repaired with wool (100 durability)

Notch pickaxe

Durability : 1753
Can dig any block
Can be repaired with diamond (1000 durability)

The old one trophy

Portable inventory portal
A portable chest which can be teleported everywhere with a spawner and teleporter

Summon item:

Ancient summoner tablet :

Recipe :
 

Tower of Flesh (ToF)

HP: 150
XP reward :100
Attack type : melee and minion, summon ToF eyeballs
Attack damage: 21
Additional information : ToF will break any block in front of it and put a under it to chase you down
↓
ToF eyeballs (hostile) 

Hp:16
Attack type : melee
Attack damage: 3
 

Loot

ToF eyeballs summon wand

Summon eyeballs minion which attack hostile mobs withshot delay 1 each 3 second
↓
ToF eyeballs minion:
Identical to the hostile version, but attack hostile mob instead

ToF scythe

Durability : 1000
Attack damage : 10
Effect | amplifier
Hunger | 2
Regeneration | 1

ToF trophy

Summon item:

Vodoo doll

Recipe:
 

Elder shulker

HP: 150
XP reward : 10
Attack type: ranged (shulker bullet) 
Attack damage : 16

Loot

Fly ability
Durability : 956
Will give you levitation effect when held

Shulker buddy Summoner

↓
Shulker buddy

Health: 60
Additional information: doesn't attack hostile mob but instead will run away from it, can be tamed with cookie to make it follow you, it has 27 inventory slot

Shulker core summoner

↓
Shulker core

Will keep placing shulker boxes on top of it, giving you unlimited shulker boxes

Summon item:

Elder Shulker geometry

Recipe:

Jungle crawler:

HP:180
XP reward:150
Attack type: melee and ranged (web projectile) 
Attack damage:17
Additional information: the projectile shot by  jungle crawler will place cobweb to slow you down

Loot

Poisonous string

As of now can only be used to make  crawler fang glove more things coming soon

Poisonous web launcher

Attack damage : 7
Additional information : shoot projectile 1 every 3 second and place a cobweb to slow your enemy down

Jungle crawler mount summoner

↓
Jungle crawler mount

HP: 45
Attack type : area damage (3 damage per tick for hostile mob within 15 block area) 
Additional information: can be tamed with spider eyes
 

Structure
Structure now spawn on the world containing the bosses summon item and some loot
Here all of them as well as the biome their spawn in

Magma king temple[nether]:

Inside view:

Elder enderman temple [overworld]

Inside view:

The old one shrine [nether]

Inside view :

Elder shulker castle [the end]

Inside view:

Sea guardian boat

Inside view:

Jungle crawler abandoned house[jungle]

Inside view:

Ghast hive [soulsand valley]

Inside view:

Version 2.0 have arrived

This update added 3 new boss , true wither, frosty, grass witch and a lot more things, here they are

True wither

Health : 1000
damage : 15
Damage type: ranged (wither dangerous)  and summon 4 tornado wither
Additional information: it's an aerial mob with ranged attack and plenty of health only attack if you prepared

Summon item:
True wither seal

Loot

Wither cultist head

Durability : 3253
Effect || amplifier
Haste || 3
Jump boost || 2
Poison || 1
Slow falling || 4
Strength || 2

Wither blade

Damage: 15
Durability: 3000
Additional information : if you hold your screen/right click it will summon wither skeleton to help you up fighting

True wither trophy block

Wither turret

Damage : 6
Health : 50
Damage type : range and explosive
Additional information : this is a stationary mob that will attack any monster although be careful since te projectile by this mob can destroy block with it explosion

Tornado wither

Health : 20
Damage : 6
Damage type: melee
Additional information : an aerial mob, it attack you with melee while flying

Wither fog

Health : 30
Damage : 6
Damage type : melee and summon
Additional information : the source of tornado wither so be sure to kill it first before it overwhelmed you

Grass witch

Health : 325
Damage : 3
Damage type : melee, range, summon
Additional information : it could attack you by charging you and attacking you melee or range if you got hit by the ranged attack it would spawn a grass trapper under you, and it could summon spore and grass spike

Summon item:

Mossified magic stick

Loot

Grass sword

Damage : 10
Durability : 3564
Additional information : it could place grass trapper in either of your side to protect you when you hold your screen / right click

Grass trapper spell book

Damage : 5
Delay per shots : 5 second
Additional information : when hit something it will place grass trapper block under the mob

Grass witch trophy

Spore

Health : 40
Damage : 3
Damage type : melee
Additional information : mossified corpse summoned by grass witch

Frosty

Health : 400
Damage : 3
Damage type : melee, ranged and summon
Additional information : it place snow layer under it, summon frosty minion (snow golem but hostile)

Summon item:

Sinister snowball

Loot

hat and scarf

Durability : 459
Additional information : give effect
Effect || amplifier
Absorption || 4
Haste || 2
Speed || 2

Snowman spawner

Delay per shot : 3 second
Additional information: spawn snow golem minion

Super Snowball

Damage : 8
Delay per shot : 1 second
Additional information : a very beefed up version of snowball, the power(velocity) is 100, doesn't affected by gravity

Frosty snow golem

Health: 4
Damage: 2
Damage type: ranged
Additional information: it's the same as snow golem but hostile

Trophy block view:

Here are the structure added for the New bosses with inside view: