Mistborn: Secret History (Mistborn, #3.5)

It was interesting to see the stuff Kelsier's been up to "behind the scenes".
I'd probably have enjoyed it more if the events of the first 3 Mistborn books were fresh in my mind, though.
The story was weakened a little by how there was nearly nobody for Kelsier to interact with. And, I thought, knowing that he was influencing some characters' actions weakened those characters just a little.
Still, extra insights into the cosmere are always welcome.