Green’s Dictionary of Slang

1. phencyclidine.

1979		H. Feldman et al. Angel Dust 124: The large number of street names it has been accorded over the years: [...] mist.
1981		D.E. Miller Bk of Jargon 338: mist: PCP.

2. smoke created by a crack cocaine pipe.

2001

ONDCP Street Terms 15: Mist — PCP; crack smoke in the bottom of a glass pipe.

3. (UK Und.) a state of high excitement, drug-induced or otherwise.

2004

N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 143: The mist was on me and I wasn’t about to stop. I grabbed him by the hair and tried to lift his face so I could cut him again.