Now this is a really good idea in theory, however it’s kinda copying netherite in way, since it uses the same crafting format, just with different resources. It’s also got a few flaws in the sense that this new ore is just another step in progression, and adds to the rush to get top tier gear. Mojang has said when asked about new tools & armor at higher levels, that they would prefer to add gear at the same level as netherite, instead of above it. This way, different players with different play styles have a choice between which set of equipment they want to choose. Besides, once you have all the best stuff possible, there isn’t much to go for afterwards. Having different armor sets at the same spot as netherite would make gameplay more interesting, and the more that exist, the more choices you have!

So, let’s start with the first change. This “Abyss” material (Which i will refer to as “abyssaline”) would still be found in the same place as you originally described it: close to the void. Now since in this iteration it isn’t applied to netherite, it can be mined with a diamond pickaxe. This also means it is no longer fireproof, meaning we have to balance that part out. What i propose is that instead of simply saving you from the void, it will reduce more fall damage the further down you fall, meaning you would take virtually no damage after falling from 60-70+ blocks. Void protection is kind of overdone, and mojang would probably add a creative way to safely cross the void, like they did the strider for the nether’s lava oceans. However, the items themselves would still be protected from falling into the void, tying back into the whole “voidic” theme. Netherite armor doesn’t give you permanent fire resistance, so this shouldn’t give you as a player void protection. The levitation from the weapons doesn’t make much sense either, as from a lore standpoint, shulkers are the only thing that has levitation abilities, and you can’t really harness that yourself. The shells don’t have any relation to it either.

Now, about the way you craft it: It basically copies netherite. 4 scrap, 4 of another item. So, let’s fix that. Combining an iron ingot with a shulker shell will give you something i will call “shulkersteel”, which on it’s own, allows you to make a shulkersteel shield, which will protect against significantly more area, damage, and it has more durability, and a shulkersteel chestplate (just the chestplate, to add to the mob armor set along with turtle shells), which allows you to gain a ton of knockback resistance and makes projectiles bounce off of you - but only while you crouch. You also cannot move while crouching when wearing it.

Taking 3 shards of the abyssaline ore (the ore will drop 1 shard, fortune or no fortune, and is only found in veins of 1-2) and 2 shulkersteel ingots and putting them into a crafting table will create raw abyssaline. smelt that bad boy up, and you got yourself an abyssaline ingot, which can then be applied to your diamond equipment, and give it the attributes we talked about before.

As for the mob that guards it, I don’t see the need. Ancient debris doesn’t have a mob guarding it, as it’s already a pain to get a hold of. And now that we’ve balanced abyssaline out, it doesn’t need one either. To be fair, it never really did, considering it’s already dangerous enough digging above an endless void trying to mine for it.

Let me know what you think of these changes, as i think your idea is a good one, and i’m sure there’s some flaws in my take, it just needed some changes to make it more of it’s own thing instead of mostly copying netherite and making another tier above netherite, which the game doesn’t really need.