The Yumfir is an ancient species of large, shaggy beasts. Nobody knows what's under all that fur, because they attack when you attempt to shear them.

The Yumfir itself can be tamed with wheat and given a chest.

There are other creatures besides the Yumfir, and it's not clear if they came with them, or if they hid themselves until now, but they seem like relatives of the Allay and Vex.

The first is the Irk, otherwise known as a Fiery Allay. These beings spawn solely in the Nether, but they are fairly easy to trick. Simply right-clicking on them with a Stick is enough to pacify them. Once captured, they can be placed into an empty Forge Mech to create the Forge Golem.

The Empty Forge is crafted like:

The Forge Golem can be tamed with Coal and Charcoal, but otherwise acts as a regular Iron Golem.

The other being is known as a Chortle. They specifically spawn in the Yumfirs' home dimension, The Old Lands. The Chortles can be caught with a Big Bottle, which is crafted like:

While not as strong, the Chortles vehicle is known as a Chortle-Copter, crafted like:

The Chortles are tamed with any saplings.

There are some dangers here.

The Yumfirs are neutral mobs, as well as their Elder. The Yumfir Elder is found only in the Old Lands. He is massive and spawns immediately as you enter, but is neutral too.... That being said, he will make quick work of you, even in full Netherite armor, if you decide to attack.

If you're up to the task, then the portal is made from Moss Blocks, and ignited by an Old Flame:

It's not not worth fighting the Elder, because defeating him is the only way to obtain the Pocket Yumfir, which is a baby that can't actually die.

If you somehow manage to lose the Pocket Yumfir, you can revive the Elder for a rematch by using the Old Flame on a Revival Stone, in the Old Lands. It's crafted with two Netherbrick Blocks, and seven Yum-furs (which are obtained by shearing Yumfirs):

Do you have what it takes?