It’s tense on mountain below summit - this animal is dangerous (5)
I believe the answer is:
tiger
'mountain below summit this animal is dangerous' is the definition.
'tiger' can be an answer for 'animal' (tiger is a type of animal). I'm not certain of the remainder of the definition.
'it's tense' is the wordplay.
I cannot really see how this works, but
'tense' could be 't' (abbreviation used in many dictionaries) and 't' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'on' acts as a link.
Can you help me to learn more?
(Other definitions for tiger that I've seen before include "Striped feline" , "Striped quadruped" , "One noted for stripes" , "Large feline of the forests" , "Large forest cat" .)