Fungus, with a drag, leads to great time (8)
I believe the answer is:
puffball
'fungus' is the definition.
(I know this)
'a drag leads to great time' is the wordplay.
'a drag' becomes 'puff' ('puff' can be a synonym of 'drag').
'leads to' means one lot of letters go next to another.
'great time' becomes 'ball' (I've seen this in another clue).
'puff'+'ball'='PUFFBALL'
'with' is the link.
(Other definitions for puffball that I've seen before include "Spherical fungus" , "Large mushroom" , "Large fungus" , "Fungus that discharges a cloud of spores when mature" , "Simple life" .)