Hallowed Crate

This is the pre Hardmode biome crate for the Hallow, and the awkward part is that an ordinary world has no Hallow until Hardmode starts. So you have to build one. Import Pearlstone and Pearlsand from a world that is already in Hardmode, lay down enough of it beside a body of water to flip the biome, and fish there.

Two shortcuts exist. Throwing a Divine Crate into Shimmer converts it backward into this, which is trivial once a run is deep enough to have Shimmer access. And the Celebration Mk 10 seed generates the Hallow from world creation, so on that seed you can fish one up in the first hour with nothing imported at all.

Once the Wall of Flesh is down, fishing the Hallow only produces Divine Crates and this one stops appearing. Any you saved are still openable, but they will never roll Hardmode loot no matter how late you crack them, so hoarding a stack to open later gains you nothing.

Nothing exclusive. Every group in the table is standard crate filler, the same ore, bars, potions and bait you would pull out of any pond in the world. The one structural guarantee is that a crate always contains at least one item from the upper groups, so it never opens completely empty of the useful half.

The utility potions are the only reason to open them fresh rather than stockpile. Spelunker and Obsidian Skin are worth far more during the cave run you are currently on than sitting in a chest afterward, and this is a reliable trickle of both.

No. There is no drop here you cannot get more easily somewhere else, and building an artificial Hallow before Hardmode is a lot of hauling for a stack of bars. Catch one for the collection and the research entry, then leave it alone.