Mike Mignola Builds Characters Sampler, October 2015. Mike Mignola cover art.
I got this e-book free, I think, on Comixology in August 2018--after their 2014 acquisition by Amazon but prior to Comixology's merge into Amazon.com in 2022. As with most pre-merger Comixology samplers I have, it is readable from my "Digital Content" list on Amazon but the page Amazon links as its product page shows no product and just says "Currently unavailable."
Release date info from Comic Vine. Comic Vine calls it issue "1," while my Amazon "Digital Content" page calls it issue "0."
Beyond the index & bio double page spread
the sampler collects story excerpt from the series listed in the index. The Hellboy in Hell story--"The Hounds of Pluto, Part 1 of 2"--is the only one shown with a title; judging from ad badges on each one's included cover art (w/ superimposed ad copy & artist credits), I think most of the excerpts are all from each series' first(?) trade paperback or hardcover; the B.P.R.D Hell on Earth one is from issue #135 of that series. All end mid-story.