Cool chopper that could help to get one up a mountain (3,3)
I believe the answer is:
ice axe
'that could help to get one up a mountain' is the definition.
(an ice axe might be used when climbing a mountain)
'cool chopper' is the wordplay.
'cool' becomes 'ice' (icing is a kind of cooling).
'chopper' becomes 'axe' (something which chops).
'ice'+'axe'='ICE-AXE'
(Other definitions for ice axe that I've seen before include "Mountaineer's equipment" , "which a climber may use" , "Mountaineer's tool" , "Mountaineering tool" , "Climber's tool" .)