FanficRecs Comment by Fillede Marius
Thirded by Fillede Marius. Every word is worth your time.
FanficRecs Comment by Aspie Crow
Seconded by Aspie Crow. I found every single canon to be perfectly in-character, and loved the ending where Seras beats the Slendy clone and then Alucard, in-limbo, runs into him/it particularly, as it's not only an awesome moment but also is some well-needed Nightmare Retardant by providing the idea that Slendy can, indeed, be killed.
FanficRecs Comment by The Doppler Effect
One of the (surprisingly few!) stories set during the Canon Fodder-ripe gap between the final two chapters. There are a couple original characters, but they're realistically written and are kept very secondary to the real cast. Features some good character moments, and great heaping gobs of Nightmare Fuel, particularly once The Slender Man Mythos starts getting involved.
FanficRecs Very well made and interesting
Story is well made, fitting well into the gap in the ending and epilogue. It also manages to keep characters close to their canon counterparts, apart from friendship between Seras and Heinkel which is in direct contrast to epilogue. Slender Man is treated with respect he deserves. He is not personally present in the story, but still manages to make the impact.
Story has pretty good pacing and manages remain interesting. Definitely worth the time.