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.

Feb
PoE New Discoverable Hideouts
In the Echoes of the Altas expansion, GGG added two new discoverable hideouts for you to find as you make your way through the Atlas.

Mar
PoE 3.14 Ultimatum Livestream Announcement
PoE 3.14 Ultimatum League Livestream at 1pm on April 8th (PDT). Don't forget Twitch Drops will be enabled from the start of the livestream until 9pm April 8th (PDT)

Jan
How to do Righteous Troll build in Path of Exile 2.5.x Patch
Chieftain with 9 endurances would have 13.5% regen not 15%. While chieftain would have more regen and probably a bit more damage, but he wouldn't be as tanky against physical damage.

Dec
Just a way from Grinding Gear Games to make you burn your poe currency
I love Path of Exile in the sense them Grinding Gear Games has made many good changes to the game along with it being free.

Feb
poe4orbs:Path of Exile Siege of the Atlas 3.17 Archnemesis Map Tiers
The new Atlas looks great and simple to understand, lets hope finding the endgame bosses is as simple :D. Atlas passive tree looks to be pretty interesting endgame content aswell, much better then before! Overall looks to be another great content update