Nicrosil is the external enhancement pushing metal. An Allomancer burning nicrosil is able to enhance the effects of another Allomancer's powers. Feruchemists can use nicrosil to store Investiture, and when used as a Hemalurgic spike, nicrosil steals an unknown quality.
Allomantic Use
A nicrosil Misting is known as a Nicroburst. An Allomancer burning nicrosil and touching another Allomancer will cause the latter's reserves of the metals they are currently burning to disappear and give a huge burst of power.[1] This can cause issues with metals such as tin, where the mental overload can cause unconsciousness.
Feruchemical Use
A nicrosil Ferring is known as a Soulbearer. Nicrosil is used to store Investiture. This ability is not understood (even by those who utilize it).[1]
Hemalurgic Use
When used as a Hemalurgic spike, nicrosil steals some unknown trait or quality.