Slough introduced to exotic tango -- this goes downhill fast (8)
I believe the answer is:
toboggan
'this goes downhill fast' is the definition.
(vehicle which goes downhill)
'slough introduced to exotic tango' is the wordplay.
'slough' becomes 'bog' (I've seen this before).
'introduced to' indicates putting letters inside.
'exotic' is an anagram indicator.
'tango' anagrammed gives 'togan'.
'bog' going within 'togan' is 'TOBOGGAN'.
(Other definitions for toboggan that I've seen before include "Sled with boards curved up in front" , "Snow vehicle" , "Flat-bottomed sled" , "Long light sledge for snow" , "Light sledge for sliding downhill" .)