The Immortal Snail by AlainCraftYT

An immortal snail spawns in roughly 20 blocks from you when you spawn into the world. He is slow and fairly easy to avoid if you can see him coming, but if he reaches you, instant death. Even with full prot 4 netherite with beacons, enchanted golden apples, and turtle master potions, he will kill you in a single hit. He hits so hard, he might break your armor in a single strike. 

It's best to avoid him, but should you wish to kill him, there is only one way. By killing the immortal snail's peaceful brothers and sisters in swamps and dripstone caves, you can get 3 new items: Raw Snail, Snail Shell Shards, and Ooze. Following the Raw Snail progression tree in the advancements tab brings you to a food that can give you the immortal snail's immunity for a short time. The Snail Shell Shards lead to a set of snail armor with incredible durability that can survive several hits from the immortal snail even if you don't. The Ooze tree is a little different. The immortal snail's rage grows as he sees you kill innocent, peaceful snails right before his eyes while he is too slow to stop you. The final straw is when you make a potion from the ooze of innocent snails and splash him with it. He immediately transforms into the form of his true full potential, the King Snail, and summons two Snail Knights to aid him in battle. The King Snail boss fight begins.

The snail's increased size gives him a larger reach and a powerful knockback attack. He and his knights hunt you the same way the immortal snail did, so if you are not prepared to finish this fight, be prepared to be chased by them forever. The increased size gave them one single weakness though, they are vulnerable to player melee damage. So buckle up for a long, difficult battle as you dance just outside the snail's melee range while still staying close enough to hit him. When the king finally dies, he drops an item that can be used to make a powerful helmet.

But the fight against the snails isn't over, even with the King dead, another snail may soon take up his charge and become the immortal snail again.

There is also a new snail villager profession just for fun. It's pretty expensive, but uhhh... I wanted it... The knights can also be tamed and ridden, but they're snails so they're slow and there's no real use for it.

If you start to struggle and don't know what to do in the mod, look at the advancements and check your known recipes. It should have enough info to help you figure it out

Full list of added features:

Entities

• Snail (Spawns in swamps, mushroom fields, and dripstone caves, Can be bred with red or brown mushrooms)
• Immortal Snail (Hunts you down and one-shots you)
• King Snail (Boss fight)
• Snail Knight (Spawns with King Snail and can be tamed and ridden)
• (Technically there's a baby snail entity too because I couldn't figure out how to do breeding without a separate baby model but it has no spawn egg, you'll need commands)

Items

• Snail Shell Shards (Dropped from snails)
• Snail Shells (Made with 9 Snail Shell Shards)
• Raw Snail (Raw food dropped from Snails)
• Escargot (Made by smoking Raw Snail)
• Golden Escargot (Made with 1 Escargot and 8 gold ingots)
• Enchanted Golden Escargot (Made with 1 Escargot, 4 gold blocks, and 4 Snail Shells)
• Ooze (Dropped from Snails)
• Snail Potions (Made from brewing Ooze into awkward potions)
  • (Everything connected to a normal potion system works except for the lingering potions and arrows. It didn't work when I made it so I'll need to figure it out eventually.)

Armor

• Snail Armor (Full Armor set made with Snail Shells)
• Reinforced Snail Helmet (Helmet made with Snail Hat and King Ooze)

Villager Profession

• Snail Research Table (Made with 4 planks and 2 Ooze)
• Snail Farmer (Has a full set of snail-related trades, mostly focused on spending emeralds for snail stuff since snails are kinda rare.)
  • Uses Snail Research Table as his workstation