I remember Mercy getting Play of the Games back when you could revive multiple team members with the ultimate ability. This is not longer possible, since you can only revive a single team mate.
All I can think of is killing multiple enemies with the Caduceus Blaster in quick succession. This is an extremely unlikely event.
Is there another, more realistic, way?
The Play of the Game system is mostly based on how much of the On Fire bar you accumulate. So in general your best best is to do (or boost) a lot of damage or a lot of healing within 10 seconds, and hope that no one else on the team has something better. The game also prioritizes actions done later in the game (especially overtime). I believe Mercy also gets extra fire if the person she resurrects does good immediately after, but I'm not sure.
However, there are a few other ways to get PotG that occasionally pop up, and are noted by their special subtitle.
For Mercy specifically, one not-all-that-unlikely idea is to kill a McCree, Brigitte, or Mei who's just incapacitated someone, and then heal them as much as you can afterward. Mei is probably the safest to try - keep healing the person being frozen to ensure they can survive the followup icicle, shoot the Mei, and continue healing afterward.
I got my POTG with mercy for reviving an ally (reaper),and he used his ult and got a two full kills. So that's another way!
Doing damage with Mercy can be very difficult, especially with her little pistol but, being near an enemy while healing a teammate can inflict damage on them. Try that and see how it goes. Or use the pistol.
