Hmmm... I have no recollection of this 'spook slither' chap either, for the record. I just showed the video to Mr Zebra, who would have slightly more chance of remembering early 80s stuff than I would, and he doesn't remember him either.
At the risk of going off-topic though, this has suddenly brought to mind a rather terrifying character I saw on one of those 80s clip-shows sometime last year - some extremely disturbing (to my mind, anyway) man who would wear strange clothes and appear in wardrobes... I've probably not explained that right, but my mind is giving me a mental block on any more details. Yes, it did disturb me that much.
I don't know if I ever saw this character when I was younger, but the horror of it (I'm really not joking) when I saw the clip-show evoked a slight disturbance so perhaps I did, and blocked it out back then.