My precious horror+mystery bag that I got for you from a secret organization.
AnimeSpoiler
If you want to get chills, these are the best contenders for me, all of them had at least a couple of really amazing moments that made my heart actually skip a beat, ordered from the scariest to the least but all of them are very close to each other. Sankarea last because of the less serious plot than the others at times. Although I will say, the prequel episode for it was SOOO AMAZING, that I'd recommend to check it out after, that middle episode scene really took me by surprise, even thinking about it now I get goosebumps.