Barabbas's Midrange Umbra Warlock (April 2017, Season 37)

This deck is built around Spiritsinger Umbra as you can see the various synergies with the other deathrattle cards such as Possessed Villager, Volatile Elemental, Devilsaur Egg, Twilight Summoner and Cairne Bloodhoof. Abusive Sergeant, Dark Iron Dwarf, Defender of Argus and Ravenous Pterrordax have synergy with Devilsaur Egg. I included Acidic Swamp Ooze and Gluttonous Ooze since warriors, paladins, hunters, shaman and rogue all have weapons but this card can be swapped out depending on what decks you are encountering frequently.