“Let’s skip school and go to the arcade today. YOLO!” “I don’t think so. I see ghosts all the time, so I believe in a world after death.”
In 人生は一度っきりだしな, what does だしな stand for? I suppose だ is the copula, な is “seeking agreement” and し is used as the “listing reasons” particle. Is this correct?
Second question: if the above explanation is correct, is だ mandatory, or can I also say 人生は一度っきりしな?
I think し is the grammar for listing reasons, and 人生は一度きり is a Japanese expression that means roughly “you only live once”, or in English YOLO. な is probably a variant of ね.
Your assumption is correct, だ is the copula, し is listing a reason and な is a sentence ender like ね.
But you definitely need the copula to connect っきり to し, like with nouns. You could leave out な if you wanted, though.