This is the oldest golem of the world, legend says it once fought along side with a Hero to fight against a cursed demon, They've won the battle... but at what cost?
You can find it guarding someone's grave in forest biome.
It drops 

 Sword Fragment  when defeated, which can be used to reforged:

 The Peacebringer.

He is him.
It can be found in the middle of the Ancient Spikes in ice spikes biome.
 Primordial Ice will be dropped as a reward for defeating it.

An old machine that the Piglins never had a chance to complete it.

You can find its unfinished body hanging in the Molten Forge.
It can be repaired with 4 Molten Fragments and a gold block.

Drops Gem of Blaze upon death.

 Eye of The Guardian can be used to summon a guardian that will protect you at all cost. It can be found in a new structure called Ender Shrine in The End.

They are very tough enemies, their attack ignores armor and deals a lot of damage, each of them has different abilities but synergizes very well with each other, they can wombo combo you to death quickly and easily if you are not ready for the battle. 

You can find them guarding their carriage with a ton of loot inside around the overworld.

Their movement is quite... strange.

They attack very fast.

Drop wrought steel scrap which can use to make the new armor set, lightning dagger,...

<Insert cool lore here>
This is a boss that can be found in the new structure called Wrought Fortress.

  You can find the structure via the Wrought Fortress Explorer Map which can be crafted using weird looking pumpkin, some papers and redstones. Right click this item to activate a 20 minutes challenge, it give you the position of the structure and only end when you find the fortress.

  Gem of Thunder will be dropped as a reward after you defeat Wrought Sentinal. ( This gem ability will be triggered if you get strike by lightning ). 

  Stormruler is also another reward from the boss.

This is an ancient type of Iron Golem that is stronger.

 Origin Scroll, which can be found in Woodland Mansion, Stronghold Library, Dungeon,... and Ancient City. This can be used to make the new golem type by holding Origin Scroll in your hand and right click to the pumpkin:

You can give it a chest ( Sneak and right click it with a chest in hand ) to store item.

 Natural Scroll, spawn in Origin Ruin chest, can be used to upgrade the golem:

 Demonic Scroll can also be used to upgrade the golem:

These are very strong creatures that can crush everything on their way and is immortal.
But everything has its cost, the owner of them will be cursed with endless suffering meaning any damage they take will transfer to the owner.
They will die after the owner dies.
But they will separate into two individuals and curse you once again:

They will be gone for good after you ( the owner ) die again.

You will see this mob wandering around the swarm biome, It once was a regular iron golem that get abandoned by its creator.

If one get killed when a slime or Ooze nearby, it will turn into Ooze Golem.

You see them in the swarm.

There is a 50% chance to spawn an Ooze when it dies.

Ooze can be tamed by using slime ball, you can ride it ( Holding a slime block while riding will make it goes faster ).

A tamed Ooze can be bucketed :)

Weird Looking Pumpkin:

All the Wrought Golems drop this item.

Appears near the Wrought Golems carriage.
Appears in Wandering Trader trade.

Bloodflame Rose:

Rarely spawns around The Nether.

Lightning Dagger:

Stormruler:

Peacebringer:

Recharge Primordial Ice:

Stick of Primordial Ice: 

Demonic Scroll:

Blackstone Fragment:

Gilded Blackstone Fragment:

Molten Fragment:

Molten Sawblade: