Use Zenyattas or Lucios Q right when someone on the enemy team Qs, like reapers/junkrat/pharah/roadhog/solider 76 ults, You will get the potg cause you pretty much stopped a team kill
Mercy is kind of silly how easy it is for her to get potg, just Q after a rip tire on the entire team and gg.
Tracer probably the hardest to get a potg on. Youre only going to get it if you get a triple kill with pulse bomb and someone doesnt out play that.