Dream GI nearly raised with mysterious person (6)
I believe the answer is:
enigma
'mysterious person' is the definition.
(I've seen this before)
'dream gi nearly raised with' is the wordplay.
'with' says the answer is hidden in the clue.
'raised' is a reversal indicator (going up in a down clue).
'amgine' can be found hidden inside 'dream gi nearly'.
'amgine' reversed gives 'ENIGMA'.
(Other definitions for enigma that I've seen before include "'Mystery, riddle (6)'" , "Title of Elgar's set of variations" , "Elgar Variations nickname" , "WWII cipher" , "Puzzle of gamine (6)," .)