Hello! I am doing my Yale EA app and in the supplement essay, I am considering putting a slam poetry piece I wrote a while ago about my relationship with my father. It’s a good piece, (I think) very well written. Is it too risky or would it make me stand out? After all, the prompt did ask for anything that would add to my application, whether it be experience or else 
I assume you mean RD application as the EA deadline was November 1st.
Yale does have slam poetry as a co-curricular activity (http://www.yale.edu/teethpoets/Pages/About.html), but given how much weight is placed on the supplemental essay, it’s difficult to say without reading your piece. You should ask a trusted adult in your life (not your father or mother) – maybe your recommendation writers or guidance counselor, people who know you well – if they think it’s too risky?