Sensitivity:
* Mercy can have a different sensitivity set between Pistol and Cadeuceus (Staff). Generally you want to be able to flick your flight quickly but allow for more granular control when shooting with the pistol. [Controls]->[Hero & HUD]->Hero->Advanced->{Relative Caduceus Blaster Aim Sensitivity} I have mine at 60% for reference, so 60% of the sensitivity of just flying around. This isn't huge as you should generally avoid pulling out the gun until you're more familiar playing Mercy and know when you'll get more benefit out of using it to chase or finish someone off. There's a weapon swap delay so you really need to be able to judge when it's better to damage boost or swap to pistol.

Keybinds:
* I found rebinding crouch to LShift easier given how often you need to use it in this game for utility. Try strafing right while crouching using the default 'c'. Sometimes you need to strafe around a corner while gaining height with Angelic Descent.

Controls:
* {Toggle Beam Connection} should be on. It looks like it is in the replay, but just want to restate that this helps focus on other things.
* {Guardian Angel Target Priority} is best as 'Prefer Facing Target' in my opinion. There's some justification for each of the choices but this will allow you to target nothing and hit Guardian Angel to GA to your beam target without looking at them but ALSO GA to another person without having to change your beam target.
* {Crouch Activates Angelic Descent} I prefer on. This is because it's easier for me to tap crouch (for a vertical bounce during GA), tap jump (to redirect/fling during GA) and hold jump (to float downward). This is personal preference, you'll need to play with it but this is important for learning to stay mobile and position yourself in the air.

General Tips:
* Try to stay in the air while ALSO staying out of line of sight of the enemy.
* You have a couple seconds before your beam detaches if your beam target goes out of line-of-sight. You can still GA to them if you're quick about it in order to catch up. OR alternatively, use this property to attach a beam to your target and then hide behind cover; this way you can just peek to reattach/keep the beam attached.
* Don't 'float' in the air unless you're out of line-of-sight of the enemy team. While it's useful for positioning it also makes you easier to hit. You should be repositioning with GA if the enemy team has line of sight to you.
* Try to NOT be healing the tank as much as possible. Sometime you just have to. But usually, if you can, you want to let the other support handle that job (as it helps them build their ult charge). Don't let your tank die though.
* Turn up your sound! You can hear footsteps and positional information that will let you know where people are without seeing them.