Thanks for the reply and im sorry for the lack of space. As you can tell, iv never been great at writing.
The way i imagine the strength of the shiny items is similar to the way gold and platinum, or even copper and tins item strength is.
Im not sure if the stats are different on PC, but on Xbox the defence stats for hallowed legs, chest plate and mask are 11, 15 and 24.
So, my idea would be to just slightly increase these values by 2-4 points so they aren't much better than the originals, but the added variety would hopefully make the game a slight bit more intresting. There would be a different set bonus, but i haven't thought of exactly what yet, or even what the armour would look like. The 2-4 point extra thing would also apply to the other versions of the helmets.
Weapon stats would work the same way. The excalibur does 52 damage so the shiny equivalent, which i think could be called Light's Saviour, (im not good at making up names, sorry) could do 55. Then The True version could have a projectile attack like the True Excalibur but unlike it this would have the ability to pierce 1 enemy and disappear upon hitting a second. However the projectile would only deal 3/4 as much damage to the first foe hit and only half as much to the second. Both versions of the LS would also swing slightly slower than the hallow counterparts.
As for enemies, i haven't had much luck thinking of many new ones. I guess there would be shiny slimes and shiny mummy's in the desert, and i was thinking there could be a mini boss called the Light guardian that spawns when it rains, similarly to the rainbow slime but more powerful than the frost giant or the desert storm equivalent. It could be the only above-ground enemy to drop souls of light and it has the chance to drop a new material item called Broken light bulb. Crafting it with 50 glass, 30 souls of light and 10 souls of sight would give you an equipable item that gives you a bright aura around your character which gives off a decent bit of light and pushes some incoming projectiles away from you if they're not moving too fast. This item would be combinable with others to make things like the Light bulb in a balloon or something like it. Im not sure if this accessory sounds good or not though.
All in all i guess the main reason ppl may want the shiny biome to spawn instead is just to experience new enemies or find diffrent blocks to build with. I know i haven't thought of nearly enough enemies or items yet and i didn't say a single thing about an underground part, but im out of ideas for now. I will definitely keep thinking of things to add though if people are interested and will try to come up with items for the shiny mimic to drop.
The thing with corruption and crimson is that they both have diffrent biome hazards and bosses with unique loot. Since theres no biome specific boss or land hazards for hallow im struggling to think of a good reason to hope to get the shiny biome over the hallow, except for the mimic and dungeon chest items. Although i haven't thought of what they could be yet.
Anyway, sorry for the late reply. I hope this wasn't as messy as my last message.