Tell us a bit about a biome you've had in mind. Try to add a description about the theme of the biome, what types of enemies would inhabit the biome, what kinds of dungeons/lairs would be in the biome, what class might be for that biome, etc.
A biome would be an area of Nuclear fallout.
The biome that has a new uncommon liquid called Waste. When touching waste players will either receive a random buff or debuff, mostly debuff, (Examples: energy drop, health drop, movement speed boost, 15% damage buff/debuff, jump boosts, etc.)
mutant like mobs would have their body parts hanging out of them (Ex. hand hanging on top of a head) have green/yellow liquids flowing out of their mouths. some mobs might be faster, some might be able to climb walls or other type of "Super powers" you can think of.
Some examples of dungeons/lairs you would find in this biome or nuclear power plants, giant craters, and Destroyed buildings.
A biome that would be a really deep hole in the treasure isles where you could go down to the bottom and visit giant squid lairs.
All the mob would be fish themed and very few would be able to go on land. There would also be volcanic vents that had lava-resistant enemies in them. There would also be giant angler fish instead of shadow giants. It would be sort of like the mariana trench in that it would be really deep. It would open up to a huge underwater lake when you went down the entirety of the hole. All the enemies would be able to swim unlike those underwater guys in the treasure isles.
The class for it would be some kind of creature from the black lagoon type guy who had a trident melee or something.
I have other biome ideas as a blog post.
The Towering Forest
A biome that featured a lot of enemies that could actually fly as well as ranged enemies. There would be many huge trees that could be climbed up either with springs or parkour.
There would be some nests on branches that housed lots of birds and some eggs that could be harvested as materials. There would be enchanted wood and on the ground there would be spiders ad plants. The plants would be the enemies that shot ranged attacks, the spiders would be like any other spider enemy, and there would be birds that could actually fly and dive bombed the player to attack.
Some ideas for dungeons and lairs would be a bigger than normal tree that was hollow with going on top of the tree to fight the boss, some giant nests that you could go inside and fight a giant mother bird that spawned birds, as well as a huge lake with some enemies that could actually swim around in the water like in the Deep biome mentioned above, and maybe a huge spider web that you had to climb up to get to the boss.
A really high biome with snowy type regions on the very tops and mostly brown rocky terrain. It would be so high that you could die from falling off of it. Inside the mountain there would be different caves with rock/ice enemies such as boulder enemies. The higher parts would spawn more golden souls and magic find would increase the higher you got. At the top of the mountains there would be boss levels involving you fighting a giant rock monster that would be a lesser version of a shadow titan. The class for it would be a rock climber or sherpa.
I don't know if this would count as a 'Biome', per se, but I'm suggesting it anyways.
NPC Villages. And the NPC's don't try to murder you instantly. Also, animal taming.