### Clue: Cocaine and heroin? Me? I'm a mythical creature (5,5)
### Answer: TOOTH FAIRY 
 ### Explanation: Definition: I'm a mythical creature
 TOOT(a quantity of inhaled powdered cocaine) **plus**(and) H(slang for heroin) + FAIRY(an example of which/? in English folklore is Puck/the setter, using the self-referential pronoun).