Chronium

On the outside, Chronium looks like rusty metal with copper colors. This special metal can be found only in the Timescar, a massive canyon north of Azura. Chronium is a very rare metal as the method of acquiring it means sending parties into the Timescar, which is a deadly landscape in it of itself, not counting the myriad of monsters waiting there. However, once acquired it is a valuable metal that allows the user "to manipulate time itself." Weapons are able to revert their swings, shields show up in two places at the same time or armour saving a person, "freezing" them in time. Many other uses can be found but the metal is one of the rarest and the newest one, existing only after The Second Divergence.

Properties

Weapons made from Chronium gain the ability to reroll an attack (if two d20s are rolled, the user chooses which one to reroll). This ability can be only used once per long rest and can't be used with other features that grant the same ability. Weapons made from Chronium cost ten times the base price.
Armor made from Chronium grants the user advantage on death saving throws. If the user already has this feature, he gains a reroll on the check (he chooses one die to reroll). Armor made from Chronium costs four times the base price.
Shields made from Chronium grant the ability to make an enemy attack reroll the check against them (if two d20s are rolled, the attacker chooses which die to reroll). This ability can be only used once per long rest and can't be used with other features that grant the same ability. Shields made from Chronium cost ten times the base price.