A build that focuses on the Mercy's survivability because a dead Mercy can't support the team. The whole goal is to be as obnoxious to kill as possible while staying in Valkyrie as often as possible.
Item purchase order
Round 1
When you [Resurrect] an ally, you both gain 250 Overhealth for 6s.
1,000 
When you die, gain 15% Ultimate Charge.
1,500 
While on the Objective, restore 8 Life every 1s.
1,000 Round 2
1,000 
While affected by [Angelic Descent] or [Guardian Angel], heal 3% of your Life every 1s.
4,000 Round 3
After succesfully using [Resurrect], activate [Valkyrie] for 5s.
When you spend your Ultimate Charge, grant nearby allies 75 Overhealth for 3s.
4,000 
When you use an ability, gain 25 Overhealth for 3s.
4,000 Round 4
Restore 3% of your Life every 1s.
10,000 Sell greens if you can't afford purple
Round 5
While [Valkyrie] is active, the healing and damage boost of [Caduceus Staff] are automatically applied to nearby allies.
When you die, gain 15% Ultimate Charge.
1,500 While on the Objective, restore 8 Life every 1s.
1,000 
10,000 Round 6
Prevent 15% of incoming damage and instead take that prevented damage over 3s.
11,000 Round 7
[Sympathetic Recovery] heals for 20% more and heals you even while you are healing a full health ally.
When you spend your Ultimate Charge, grant nearby allies 75 Overhealth for 3s.
4,000 When you use an ability, gain 25 Overhealth for 3s.
4,000 
The first time you would die each round, revive instead with 250 Life after 3s.
9,000 
When you take more than 100 damage at once, restore 20% of damage taken and start regenerating your Shields.
9,500 If you're not dying because you're goated, don't buy the revive (Geneticist's Vial) and instead buy Angelic Acrobatics in the purple Ability tree.
