terrible horror, I meant that
Most, but not all, of that is based on the recording techniques used, although I think a bit of 'extreme' reverb and delay may have been used in the first example. Which means basically that you have to use an 'active' mic technique with the person acting this out. Primarily, it isn't effects-based at all.
There are a few things you can try though. Altering the pitch of sounds without altering the speed, and mixing the results can sound pretty horrific, and echo effects always help, but in the end it's really a matter of manipulating what you can record - and if that isn't really horrific-sounding in the first place, then you have a lot more work to do.