Smoke methamphetamine under Dutch railway (3,3)
I believe the answer is:
dry ice
'smoke' is the definition.
(dry ice creates a smoke or mist effect)
'methamphetamine under dutch railway' is the wordplay.
'methamphetamine' becomes 'ice' (slang term).
'under' means one lot of letters go next to another.
'dutch' becomes 'd' (common abbreviation).
'railway' becomes 'ry' (abbreviation for railway).
'd'+'ry'='dry'
'ice' put after 'dry' is 'DRY ICE'.
(Other definitions for dry ice that I've seen before include "Producer of stage mist" , "Solid carbon dioxide (used for a stage effect)" , "White mist on stage" , "theatrical effect" , "may be used for effect on stage" .)