Complementary Nautilus

Have you ever looked at the nautilus shell from vanilla Minecraft and felt like something is missing?
A nautilus is a cephalopod with a spiral shell considered to be a "living fossil" more closely related to early cephalopods than other modern species.

Features:

• The purpose of this mod is very straightforward: to add a nautilus mob to complement the item.
• They will spawn rarely in any biome specified by the tag: data/nautilus/tags/worldgen/biome/spawns_nautilus.json
• By default, this will be the ocean, lukewarm ocean, deep ocean, and deep lukewarm ocean biomes.
• They drop exactly one nautilus shell.
• The swimming motion is based on that of fish, but slightly faster to escape players.
• Out of water, they will fall over onto their side.

I know the nautilus shell is supposed to be a rare item for crafting a conduit or trading for a trident. However, some players might find it too uncommon._