Linking sci-fi movie up with horror movie (9)
I believe the answer is:
tethering
'linking sci-fi' is the definition.
I can't judge whether this defines the answer.
'movie up with horror movie' is the wordplay.
'movie' becomes 'ET'.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'with' is a charade indicator (letters next to each other).
'horror movie' becomes 'thering' (I can't explain this - if you can you should give a lot more credence to this answer).
'et' in reverse letter order is 'te'.
'te'+'thering'='TETHERING'
Can you help me to learn more?
(Other definitions for tethering that I've seen before include "Securing" , "Restricting, in a way" , "Tying up an animal" , "fixing in position" .)