Magic is a slang term for a mix of heroin and fentanyl. Fentanyl is a synthetic opiate approximately eighty times as strong as morphine. It is an odorless white powder that, because of its strength, is often used to "cut" low-grade heroin to increase potency. Magic, also known as "The Bomb," is an incredibly dangerous type of heroin, and is extremely easy to overdose on.
"Hey man, did you hear that Big Joe OD'd on some Magic last night?"
"Shit man... give me black tar any day, I won't go near that shit."