Don’t aim to beat boss before timer expires. Without a good team that’s fast it’s likely you will need to complete boss with zero deaths. Be prepared to 1 or 2 man the end if a teammate falls after timer expires. As others mentioned - builds that prioritize taking damage or healing - learn the mechanics and path on normal mode first - when timer expires whoever is the closest to boss or whomever knows jumping puzzle (likely same player) continues and pulls everyone - don’t give up