"Angel" or "Cleric" chosen with Arcane Adaptation.
Steps
Activate Lightning Greaves' equip ability by paying ({0} magic symbol) , attaching it to Priest of Fell Rites.
Activate Priest of Fell Rites by paying three life, tapping and sacrificing it, returning Necrotic Ooze from your graveyard to the battlefield.
When Necrotic Ooze enters the battlefield, Righteous Valkyrie's first ability triggers, causing you to gain life equal to Necrotic Ooze's toughness.
Activate Lightning Greaves' equip ability by paying ({0} magic symbol) , attaching it to Necrotic Ooze.
Activate Necrotic Ooze by paying three life, tapping and sacrificing it, returning Priest of Fell Rites from your graveyard to the battlefield.
When Priest of Fell Rites enters the battlefield, Righteous Valkyrie's first ability triggers, causing you to gain life equal to Priest of Fell Rites' toughness.