Sulfur Depths - this mod adds a new biome to the game - the Boiling Caves.

Requirements (for biome generation):
TerraBlender mod

Resource pack (optional)

New blocks:

Cinnabar and Sulfur - which can be crafted into other decorative blocks using a workbench or stone cutter. Additionally, if you smelt any sulfur block using a campfire or fire, it will turn into a heated sulfur variant (more orange and more durable). 

The potent sulfur block - which spawns at the bottom of sulfur lakes - inflicts nausea on the player if they swim in water containing this block, and if they are completely submerged, it inflicts poisoning and blindness.

New items:
Glob of mercury - obtained by smelting a Cinnabar block (smelting Sulfur produce gunpowder) and causes nausea if kept in your inventory - used to feed a Sulfur Slime
Mercury bottle - allows you to double the signal strength of Redstone dust by right-clicking (if it is already powered) 
Mercury bucket - allows you to pour a new type of liquid - mercury, which is very dense but highly toxic
Mercury Mirror - allows you to spotlight all entities nearby for a few seconds
Sulfur Bomb - this item can be thrown to create a small cloud of smoke on the ground that inflicts blindness on everyone inside

New mob - Sulfur Slime

The main mechanic of this mob is its ability to hold any block in the game (mod blocks are also supported) and push it using the push command, but some blocks give it special properties:
1) All types of wool - makes it lighter
2) All types of stone (including deepslate) – make it heavier, but if pushed toward a mob or player, it deals minor damage
3) Pointed Dripstone - if pushed toward a mob/player, the slime will deal double damage depending on what the player used to strike (if the item is enchanted, this is also taken into account)
4) All light-emitting blocks - turn the slime into a light source (dynamic)
5) Anvil and Obsidian - make it very heavy, and if dropped from a height (very fast fall speed), it will deal damage to a mob/player like an anvil
5) Lure blocks - an emerald block lures villagers, a gold block lures piglins
6) Damage blocks - Magma ignites nearby entities and creates fire when pushed; cactus deals damage to everyone nearby
7) Amethyst block - creates a beautiful sound when struck
8) Redstone block - activates all nearby mechanisms and activates redstone dust (if very close)
9) Copper block - if it’s a regular copper block, slimes are slightly heavier than usual; if it’s oxidized and struck by lightning, the oxidation disappears and it becomes very light
10) Ice blocks - the slime doesn’t bounce off the ground when hit, but slides across it
11) Cursed blocks - if the target is a block, all nearby projectiles will be magnetically drawn to the sulfur slime; dynamite - if dropped from a height, it will explode upon contact with a block
12) Honey block - makes the sulfur slime very sticky (it sticks to walls)
Slime block - makes the slime very elastic
13) Music blocks - a note block plays a sound when struck (instrument blocks are supported); a Jukebox allows music disks to be played inside the mob
14) Workstations - all workstations and workbenches are fully functional inside this mob
15) Storage blocks - all storage blocks (chests, barrels, and shulkers) are functional inside this mob, and the Ender Chest also works 
16) Sculk sensor - moves forward if there’s a mob nearby making sounds

Additional Features
If you set any sulfur block on fire, the flames will be blue.
You can collect Sulfur Slime in a bucket.
In the Boiling Caves biome, there is a constant thick yellow fog with ambient sound. 
Geysers are generated above the biome that can launch the player into the air