A seemingly illicit substance, usually of a white and powdered composition or occasionally with a yellowish hue.

A mystery bag is usually found in a zip locked baggie during clean up following a rave, a chance but rather delightful encounter. More deliberate encounters may come from a Boom Boom partyboy in the fall out of a festival... Boom Boom will want to keep the party going through Monday.
Yo Brains, check out the mystery bag I just found. Think I got me some chaz to keep the party going, fancy a line?

Eh I'm not so sure about that Boom Boom, it looks a bit weird

Ah screw that Brains ya dry shite

Sniff sniff

Shit, feels like my face is falling off, what the hell was that?

Haha you clown Boom Boom, it's 2ci and the bus home is just about to leave, buckle up😉
by Mysteryb87 May 27, 2019
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Sausages. So called because who knows what is inside. Sometimes meat. (Rare)
I had a couple of mystery bags with sauce for lunch. At least I kept the sauce down.
by Richard Kopf November 21, 2007
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Finding an unknown object and t-bagging it.
Tim: What's that?
David: I don't know
Tim: *T-bags it*
David: MYSTERY T-BAG!!!
by OhMehDamn July 18, 2011
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