An Alivened is a type of Golem created by Dark Oculators. They have glass parts which are keys to their being functional. The most powerful ones are referred to as Codexians and are made of paper. They guarded the library that held the Sands of Rashid.
They are extremely strong and relatively fire resistant. They can manipulate the mass of their bodies, regenerating limbs. This does cause them to shrink in size.
Alivened are created by Dark Oculators who give up some of their humanity and invest (note that this book is non-cosmere and has nothing to do with investiture) it in the object to be Alivened. This removes some of the good human qualities from the Dark Oculator, but the Alivened object does not retain these good qualities -- they are twisted and evil instead. Codexians are made out of bad romance novels because they can soak up emotion, making them especially powerful.
Members of the sect of librarians called the Scrivener's Bones have a penchant for replacing some of their body parts with alivened parts. A notable example of this is Kilimanjaro, who replaced a full half of his body with alivened metal. This sect sees not only the stronger material as an advantage, but the removal of humanity as well.