Okay, AppleOfOurEye. The Slender Man first appears at the end of episode 5.
https://youtu.be/dECFQiHTykI
My favorite episode is #8 "things that go 'flash' in the night".
https://youtu.be/mKT4cTpyseM
Besides these it is a well put together series. I do not think that there will be anymore episodes, but it is well worth a watch.