Mercy has two control customizations: Toggle Beam Connection and Guardian Angel Prefers Beam Target.
This makes using Guardian Angel as an escape route a little tricky, and if you’re using the toggle beam, you probably don’t want to lock yourself to using your beam target as your Guardian Angel target as well.
One of the most useful of the special Hero control customization’s is Lucio’s Hold to Crossfade.
Normally, to wall-climb, the player needs to hit space as the character hits the wall, then hold space to climb.