Harpy synergy

[Deebiia]

 {Abhorrent Overlord} {Gift of Immortality} Just have a build up of black devotion.

Or the other mini-combo  {Gray Merchant of Asphodel} and  {Gift of Immortality}

[Steerpike]

And if you're playing mono black, {Rescue from the Underworld} lets you sac and bring back the same creature as well.

[Moocow4u2]

Strionic resonate that for a second activation of his harpy effect