Earth & Water is a mod that expands on elemental mobs. Minecraft has the Blaze and Breeze, which fills in half the elemental mobs. E&W adds the other two elemental mobs, the Bore and Brine! These two mobs come with their own blocks and structures that fit them respectively.

Bore

Think Blaze or Breeze.. but Earth. The bore is a protective mob who wants you away from it. Bores spawn in Ancient Ruins. If one catches you spelunking in its territory, it'll shoot out a Earth Charge at you. These Earth Charges fracture on impact and hurt, a lot. If you get too close, it'll try burrowing in the ground to get away. You can of course dig it up with a pickaxe if you catch up to it.

The Bore, or Earth part of E&W, comes with:

Bore Rod Item
Earth Charge Item
Dripstone Brick Set
Dark Dripstone
Dark Dripstone Brick Set
Ancient Ruins Structure

Brine

The other Blaze/Breeze type mob. The Brine lurks in the depths of the ocean in the Conduit Monument. They dash through water to get around, and are quite fast. It shoots out a Water Charge, which in short is a sticky bomb. Stays where it was thrown for two seconds, then blows up, sending everyone in the radius a great distance. Brines are friend of the Conduit, for the Conduit doesn't try hurting it.

The Brine, or Water part of E&W, comes with:

Brine Rod Item
Water Charge Item
Prismarine Tile Set
More Dark Prismarine Blocks
Oxygen Block
Conduit Monument Structure

Battle Axe

Crafted with Steel and Bore Rods, the Battle Axe serves many purposes for its user. Those who use it can dash forward and slice any enemies in its path. Speaking of dashing, it travels about 3-4 blocks in the direction its user looks, allowing one to escape swiftly from any conflict.

Whip

The Whip is a weapon primarily used underwater. When attacking underwater, you apply a short stun to whoever or whatever you hit. When stunned, it slows and weakens you, so it is best to stay away from those with whips.

Spiked Shield

The Spiked Shield is quite self-explanatory, but regardless.. The Spiked Shield, when hit, sends 3.5 hearts of damage right back at its attacker. One can obtain this shield by putting a Shield, a Spiked Shield Upgrade Template, and a Steel Ingot into a smithing table. You can customize these shields with banners too!

Reinforced Spawner

You know how 1.21 added Trial Spawners? Well the Reinforced Spawner is almost like the Trial Spawner, but infinite. This block spawns infinite waves of the mob inside of it. Unlike the Spawner block, the waves have to be completely killed before the next one spawns. It can be turned on and off using the Reinforced Key. They are found in the Ancient Ruins and Conduit Monument structures.

Steel

Steel, a sort of "upgraded" iron. Used to reinforce the Reinforced Spawner, spike the Spiked Shield, and create the battle axe. You can find steel nuggets in Ancient Ruins and Conduit Monument structures. Nine of nuggets can create you the Steel Ingot.