used in 嗎啡|吗啡[ma3 fei1]

(question particle for "yes-no" questions)

variant of 幹嘛|干嘛[gan4 ma2]

(neologism, attested by 2014) (slang) Are you interested? (originally an invitation for casual sex, later generalized as a playful or humorous invitation for any activity)

isn't that so?