I just played my first quick play (after weeks of sporadic AI Training). Damn, playing with anxiety is tricky (sweat, gym clothes while gaming and a towel on the chair).
Any tips for playing as Mercy? I try to stay near the payload and the group, buffing the tank until I need to start healing, but if somebody gets too far away, I can't do nothing for them despite seeing them as critical. I have enabled the health bars to always be visible.
BTW, the healing ray works across walls? I'm not sure if it happened like that...
Stick near the group but try to stay out of sight. Keep mindful of the battlefield and be prepared to escape if a flanker like Tracer or Genji targets you. Try to damage buff the most effective ally within your range if no one needs healing, but prioritise healing outside of specific circumstances like an allied Soldier ult or if there's another healer on your team already taking care of someone. Sometimes people overextend and get into situations where you flying in to save them will just get you both killed. Sometimes it's better to let someone die than have your team stuck without a healer while you run back from the spawn room.
Learning to resurrect well is also an acquired skill. Sometimes it's worth flying into a group of dead allies and resurrecting them even if you know you'll likely die and sometimes it can be worth a single ally res if you think that ally can tip the scales in your favour. It's a per-situation-basis
The most useful skill as a Mercy player is to be aware of the battlefield, your allies and their capabiltiies, your potential routes of escape and who is targeting you at any given time. Being able to make good judgments based on that information is key to playing Mercy well.
Sometimes you'll have matches where your entire team is split up, you're being mercilessly hunted by a Tracer or Genji, everyone will be bugging you for healing yet refusing to get in your line of sight so you can fly to them, and you'll feel like ripping your hair out. Just stay calm in these situations, even if you probably won't win.
Healing beam works through walls for a few seconds after line of sight has been lost, but shuts down after that. It's useful to know since it can often save an ally or yourself