Nether

Miscellaneous
Nether portals can be made from either Obsidian or Crying Obsidian, not both (corners don't count). A portal made of one block cannot link up with one of a another.

Nether portals can only be generated in the top section of the nether while first entering the dimension, though they can be built and lit in any section.

World gen changes
Nether generating height is tripled (at the cost of being able to build over the bedrock ceiling) and is "split" into 3 parts (each 128 in height). the top 2 thirds are mostly the same, while the bottom third is mostly lava ocean.

Biomes
similarly to the overworld, biomes are now significantly larger and blend together much more smoothly

New Mobs
Sinker

Bubbler

Bone Serpent

Ghastling (Baby Ghast)

Piglin Scout

Piglin Cheif

Blocks
Soulstone (stairs, slabs, walls)

Soulstone Bricks (stairs, slabs, walls, cracked, chiseled)

Cursed Soulstone (stairs, slabs, walls)

Cursed Soulstone Bricks (stairs, slabs, walls, cracked, chiseled)

Blue Nether Bricks (stairs, slabs, walls, cracked, chiseled)

Red Nether Bricks (stairs, slabs, walls, cracked, chiseled)

Netherrough Bricks (stairs, slabs, walls, cracked, chiseled)

Soul Quartz Block (stairs, slabs, walls)

Soul Quartz Bricks (stairs, slabs, walls, cracked, chiseled)

Dragon Quartz Block (stairs, slabs, walls)

Dragon Quartz Bricks (stairs, slabs, walls, cracked, chiseled)

Rose Rock

Netherrough

Boom Stone

Rust Block

Glowstone Thumpets

Holy Glow

Ancient Fire

Materials
Ruby

Liquid metal (Iron, Gold, Copper)

Bedrock Quartz

Soul Quartz

Warped Wart

Rust Root

Rage Rod (Rage Powder)