When the creature dies, Bishop of Wings' second ability triggers, creating a 1/1 Spirit creature token.
When the Spirit token enters the battlefield as an Angel due to Maskwood Nexus, Bishop of Wings' first ability triggers, causing you to gain 4 life.
Resolve the Yahenni ability.
Repeat.
This clever loop turns Yahenni, Undying Partisan into a relentless sacrifice engine, protected by its own ability to gain indestructible on demand. Maskwood Nexus is the secret glue here, reshaping all your creatures into every type—including Angels—so that every token that hits the board or heads to the graveyard interacts with Bishop of Wings. As Bishop of Wings pumps life into your total each time a Spirit enters and replaces it with a new token upon death, you spin up a virtually endless cycle of sacrifices, lifegain, and triggers to overwhelm your opponents.