Uniques are not all of the same rarity
When an item is generated rarity is determined first, it can be white, magic, rare or 1 of some number of unique rarity bands. exactly how many tiers of unique there are has not been publicly revealed.
If the item is unique, a unique is chosen from the chosen unique tier.If the item is not unique, then base type etc is determined.
In the case of chancing, base type never needs to be determined. however if a unique tier is chosen for which no unique of that base exists, then the item defaults down to a rare. So the existence of multiple uniques for a base only affects the probabilities of getting those uniques if more than 1 is on the same tier list.
So to be clear, in a world where infernal mantle did not exist, the chances of getting shavs would remain the same. All that would happen is you would get a rare on those rolls where you would have gotten infernal mantle.

Dec
Path of Exile Flashback Guides and Builds
In order to help players experience the game better, this Path of Exile Flashback guide introduces the content of flashback in detail and recommends popular builds

Dec
[Mayhem] Buy Cheap PoE Currency with Fast Delivery
Buy cheap mayhem currency in Poe4Orbs to help you defeat these powerful enemies. Poe4Orbs is the best place for you to buy poe currency, safe and fast, 24/7 online support.

Sep
Path of Exile 3.12 Heist Preview
A preview of the next season of Path of Exile has been released, called Heist. PoE 3.12 Heist will add a lot of content to the game, including npcs and brand new items. Let us know the latest information of PoE 3.12!

Jul
New Player Should Never Play HC
I have performed mostly HC in each and every game which has it, I began PoE HC also it was great when Used to do. Hell, I even find Invasion is the most enjoyable time I have ever endured within this game

Nov
This means you now have legacy items
What you're thinking of is something along the lines of Legendaries from other games, which are the super GG items that have no better equivalent and are very rare.

Mar
poe4orbs:PoE 3.10 Delirium Shadow Popular Starter Build
PoE 3.10 has arrived! Are you ready to take on new challenges? Take a look at the PoE 3.10 Delirium Shadow Builds (Assassin, Saboteur, Trickster) prepared by R4pg for you!