Guy, large one having scales go up on this? (4,6)
I believe the answer is:
rope ladder
'go up on this?' is the definition.
(you can climb up a rope ladder)
'guy large one having scales' is the wordplay.
'guy' becomes 'rope' (I've seen this before).
'large' becomes 'l'.
'one having scales' becomes 'adder' (adders have scales).
'rope'+'l'+'adder'='ROPE-LADDER'
(Other definitions for rope ladder that I've seen before include "not a stiff route to the top" , "Something to get you down" , "Shaky steps" , "etrier" .)